NIMP| Silviu POLOSAN, Author at NIMP

Projects

1. Highly conductive and transparent metallic electrodes for Organic Light-Emitting Diodes

Project Type: PED 726, Start Date: 2022-06-21 End Date: 2024-06-20

2. Dual emitters for displays based on oled compounds.

Project Type: IDEAS, Start Date: 2011-10-01 End Date: 2016-10-01

Publications

1. Charge transport mechanisms in free-standing devices with electrospun electrodes

Authors: Ciobotaru, IC; Polosan, S; Enculescu, M; Nitescu, A; Enculescu, I; Beregoi, M; Ciobotaru, CC

Published: SEP 24 2022, NANOTECHNOLOGY, 33, 395203, DOI: 10.1088/1361-6528/ac7ac1

Embedding electronic and optoelectronic devices in common, daily use objects is a fast developing field of research. New architectures are needed for migrating from the classic wafer- based substrates. Novel types of flexible PMMA/Au/Alq(3)/LiF/Al structures were obtained starting from electrospun polymer fibers. Thus, using an electrospinning process poly (methyl metacrylate) (PMMA) nanofibers were fabricated. A thin Au layer deposition rendered the fiber array conductive, this being further employed as the anode. The next steps consisted of the thermal evaporation of tris(8-hydroxyquinolinato) aluminum (Alq(3)) and aluminum deposition as the cathode. The Au covered PMMA nanofiber layer had a similar behavior with an indium tin oxide film i.e. low sheet resistance 10.6 omega/sq and high transparency. The low electrode resistivities allow an electron drift mobility of about 10(-6) cm(2) V-1 s(-1) at a low applied field, similar to the counterpart structures based on thin films. Concerning the relaxation processes in these structures, the Cole-Cole plots exhibit a slightly deformed semicircle, indicating a more complex equivalent circuit for the processes between metal electrodes and the active layer. This equivalent circuit includes reactance equivalent processes at the anode, cathode, in the active layer and most probably originates from the roughness of the metallic electrodes.

2. The Synergistic Effect of the Laser Beam on the Thermionic Vacuum Arc Method for Titanium-Doped Chromium Thin Film Deposition

Authors: Vladoiu, R; Mandes, A; Dinca, V; Ciupina, V; Matei, E; Polosan, S

Published: APR 2022, COATINGS, 12, 470, DOI: 10.3390/coatings12040470

Laser-Induced Thermionic Vacuum Arc (LTVA) provides a better way to produce uniform metallic thin films than the classical Thermionic Vacuum Arc (TVA) method. In Ti-doped chromium thin films produced using LTVA, the amorphous chromium is superimposed with small bcc chromium nanoparticles. These amorphous/crystalline structures with small crystallites induce lower roughness and electrical resistivity, reducing electron-phonon scattering and increasing charge transport across LTVA thin films. A significant shift in resistivity for the LTVA samples is observed due to electron scattering on the phonon-crystalline structures in the TVA samples which exhibit larger crystallites. Meanwhile, the wettability measurements reveal a higher contact angle, resulting in a lower surface free energy and consecutively lower dissociation energy for the LTVA-produced thin films than the TVA samples.

3. Magnetic Core-Shell Iron Oxides-Based Nanophotocatalysts and Nanoadsorbents for Multifunctional Thin Films

Authors: Musat, V; Stanica, N; Anghel, EM; Atkinson, I; Culita, DC; Polosan, S; Crintea, L; Ceoromila, AC; Buruiana, CT; Carp, O

Published: MAY 2022, MEMBRANES, 12, 466, DOI: 10.3390/membranes12050466

In recent years, iron oxides-based nanostructured composite materials are of particular interest for the preparation of multifunctional thin films and membranes to be used in sustainable magnetic field adsorption and photocatalysis processes, intelligent coatings, and packing or bio-medical applications. In this paper, superparamagnetic iron oxide (core)-silica (shell) nanoparticles suitable for thin films and membrane functionalization were obtained by co-precipitation and ultrasonic-assisted sol-gel methods. The comparative/combined effect of the magnetic core co-precipitation temperature (80 and 95 degrees C) and ZnO-doping of the silica shell on the photocatalytic and nano-sorption properties of the resulted composite nanoparticles were investigated by ultraviolet-visible (UV-VIS) spectroscopy monitoring the discoloration of methylene blue (MB) solution under ultraviolet (UV) irradiation and darkness, respectively. The morphology, structure, textural, and magnetic parameters of the investigated powders were evidenced by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, Brunauer-Emmett-Teller (BET) measurements, and saturation magnetization (vibrating sample magnetometry, VSM). The intraparticle diffusion model controlled the MB adsorption. The pseudo- and second-order kinetics described the MB photodegradation. When using SiO2-shell functionalized nanoparticles, the adsorption and photodegradation constant rates are three-four times higher than for using starting core iron oxide nanoparticles. The obtained magnetic nanoparticles (MNPs) were tested for films deposition.

4. Electronic and transport properties of the dual-emitter organometallic compound IrQ(ppy)(2)

Authors: Polosan, S

Published: JUN 14 2021, JOURNAL OF ORGANOMETALLIC CHEMISTRY, 942, DOI: 10.1016/j.jorganchem.2021.121814

The structure of the IrQ(ppy)(2) organometallic dual phosphorescent compound was experimentally and theoretically investigated. The Metal-to-Ligand Charge Transfer toward the phenylpiridine and quinoline ligands explains its dual phosphorescence property. The IrQ(ppy)(2) organometallic's electronic properties extend the absorption spectra toward the lower energies than Ir(ppy)(3) due to the bandgap reduction induced by the quinoline ligand. The magneto-optical measurements reveal A-terms, which are produced by splitting the triplet states and B-terms, which arise when the electronic levels are mixed in the magnetic field. The IrQ(ppy)(2) molecule's transport properties confirm an ambipolar character, consisting of a higher hole transport character induced by the phenyilpiridine ligands and a lower electron transport character induced by the quinoline ligand. (C) 2021 Elsevier B.V. All rights reserved.

5. Highly Conductive Carbon-Based Thin Films Produced by Low-Energy Electron Irradiation

Authors: Ciobotaru, CC; Ciobotaru, IC; Iosub, DG; Polosan, S

Published: OCT 2021, JOURNAL OF ELECTRONIC MATERIALS, 50, 5541, DOI: 10.1007/s11664-021-09058-5

Highly conductive carbon-based thin films have been produced by low-energy electron irradiation. Low-energy electron irradiation at a lower density of electrons eliminates the sp(3) hybridization of the carbon atoms by reducing the chemical groups on the surface. Irradiated carbon-based thin films became highly conductive layers that could be used as electrodes for optoelectronic devices. The electrical conductivity sigma reached 3 x 10(4) S/m in the case of samples irradiated at a lower density, with a mean value between 3 x 10(5) S/m and 3.3 x 10(2) S/m for highly crystalline graphite structures. The increasing (002) peak diffraction and decreasing intensity ratio ID/IG in the Raman spectra as well as the decreasing bandgap in photoluminescence measurements demonstrated the reduction of oxygen-induced defects in these thin films.

6. Structural features, magnetic and ferroelectric properties of SrFe10.8In1.2O19 compound

Authors: Turchenko, V; Kostishin, VG; Trukhanov, S; Damay, F; Balasoiu, M; Bozzo, B; Fina, I; Burkhovetsky, VV; Polosan, S; Zdorovets, MV; Kozlovskiy, AL; Astapovich, KA; Trukhanov, A

Published: JUN 2021, MATERIALS RESEARCH BULLETIN, 138, DOI: 10.1016/j.materresbull.2021.111236

The effect of temperature on the features of the crystal and magnetic structures, as well as the magnetic properties of the solid solution of SrFe10.8In1.2O19 hexaferrite was investigated. The appearance of ferroelectric properties was detected at room temperature, which contradicts the generally accepted opinion on the description of the crystal structure of hexaferrites within the framework of the centrosymmetric P6(3)/mmc (No. 194) space group. The reasons of spontaneous polarization in solid solutions of hexaferrites remain controversial. No deviation from the collinear magnetic structure was found in the investigated temperature range from 1.5 to 350 K, while the thermal expansion of the unit cell was practically absent in the range from 1.5 to 50 K. The crystal structure of hexaferrites was considered in the framework of both centrosymmetric P6(3)/mmc and non-centrosymmetric P6(3)mc space groups, which allowed us to associate the emerging spontaneous polarization with unequal distortions of neighboring oxygen polyhedra.

7. The origin of the dual ferroic properties in quasi-centrosymmetrical SrFe12-xInxO19 hexaferrites

Authors: Trukhanov, AV; Turchenko, VA; Kostishin, VG; Damay, F; Porcher, F; Lupu, N; Bozzo, B; Fina, I; Polosan, S; Silibin, MV; Salem, MM; Tishkevich, DI; Trukhanov, SV

Published: DEC 15 2021, JOURNAL OF ALLOYS AND COMPOUNDS, 886, DOI: 10.1016/j.jallcom.2021.161249

The local crystal/magnetic structures of the SrFe12-xInxO19 solid solutions (x = 0.1; 0.3; 0.6 and 1.2) were investigated using neutron powder diffraction. The measurements of the electric polarization for all investigated samples were carried out as a function of the external electric field. The presence of the ferroelectric and ferromagnetic ordering (dual ferroic ordering) in the SrFe12-xInxO19 hexaferrites at 300 K was found. This appearance contradicts to the conventional opinion describing their crystal structure (centrosymmetric space group P6(3)/mmc (No. 194)). The reason for the existence of a spontaneous polarization (nonzero dipole moment) in the SrFe12-xInxO19 hexaferrites continues controversial. The crystal structure of the hexaferrites was considered both the centrosymmetric P6(3)/mmc and non-centrosymmetric P6(3)mc space groups. This fact made it possible to find a connection between the emerging dipole moment and not equal distortions of the neighbor oxygen polyhedral. The nature description of the nonzero dipole moment formation in a quasi-centrosymmetrical system of the In-substituted SrFe12-xInxO19 hexaferrites was presented based on the neutron diffraction data. (C) 2021 Elsevier B.V. All rights reserved.

8. Magnesium-silver cathodes for efficient charge injection into Organic Light Emitting Diodes deposited by LTVA method

Authors: Vladoiu, R; Mandes, A; Dinca, V; Kudrna, P; Tichy, M; Polosan, S

Published: JUL 15 2021, JOURNAL OF ALLOYS AND COMPOUNDS, 869, DOI: 10.1016/j.jallcom.2021.159364

The Laser-induced Thermionic Vacuum Arc method was applied to optimize magnesium-silver (Mg:Ag) alloys, which can be potentially used as stable metallic cathodes for optoelectronic devices. Besides lowering the cathode work function given by the magnesium that improves the electron injection, Mg:Ag alloys induce a higher electrical conductivity, estimated here to be 3.42 x 10(7) S m(-1) for AgMg3, compared with 2.64 x 10(7) S m(-1), estimated here for Mg thin films. Mg:Ag alloys avoid the critical issue of Mg oxidation for better charge injection in optoelectronic active layers. By improving the Thermionic Vacuum Arc technique with the laser beam, this method enables the control of the silver concentration in these alloys due to photonic processes. The uniformity of metallic thin films, compactness, and high purity are the primary advantages of the Laser-induced Thermionic Vacuum Arc method. (C) 2021 Elsevier B.V. All rights reserved.

9. Structural, magneto-optical and dielectric properties of phosphate tellurite glasses

Authors: Polosan, S; Ganea, P; Nitescu, A

Published: NOV 2021, MATERIALS RESEARCH BULLETIN, 143, DOI: 10.1016/j.materresbull.2021.111455

Phosphate tellurite glasses, with a nominal composition of 40%ZnO+40%P2O5+20%TeO2, have been synthesized by melt quenching procedure. P2O5 can lead to chemically stable phosphate tellurite glasses, compared with those classical synthesized with H3PO4. Magneto-optical measurements have shown a derivative A(1) term centered at 532 nm originating from a transition to a degenerated excited state associated with tellurium colloids. The glass densities, measured by the Archimedes method at room temperature, display an increasing value with the melting temperature of the samples. The electrical conductivity shifts toward lower frequencies with the increased melting temperature, being influenced by the mobile charges, which require lower thermal activation energy due to the Te-o metallic particles. Together with dielectric constant, the electrical conductivity underlines structural changes, by increasing the melting temperature, associated with the presence of Te-o nanoclusters.

10. Synthesis and characterization of magnetic oxide nanoparticles and corresponding thin films for wastewaters treatment

Authors: Crintea, L; Musat, V; Polosan, S; Cantaragiu, A; Basliu, V; Dediu, A; Dinica, R

Published: JUL 2020, OVIDIUS UNIVERSITY ANNALS OF CHEMISTRY, 31, 131, DOI: 10.2478/auoc-2020-0021

Industrial wastewater can be properly treated using nanotechnologies and nanomaterials. This paper presents the synthesis and characterization of three series of magnetic nanoparticles (MNPs) and corresponding thin films, used for the degradation of organic compounds and removal of heavy metals from industrial wastewater. The samples were obtained by co-precipitation from a ferric (Fe3+) and ferrous (Fe2+) ions solution in a molar ratio of 2:1, at temperatures between 80-95 degrees C. The characterization of the samples was performed by scanning electron microscopy (SEM), and X-ray diffraction (XRD) methods. The magnetic nanoparticles were deposited on glass substrates by the centrifugal coating technique and the optical and magneto-optical activity was investigated by UV- Vis spectroscopy and magnetic circular dichroism technique (MCD). The effect of the investigated samples on the decomposition under UV irradiation of organic dyes was monitored by UV-Vis spectroscopy. Our preliminary results have shown that the magnetite and maghemite MNPs can be effective in UV degradation of methylene blue (MB) dye.

11. Detailed Molecular and Structural Analysis of Dual Emitter IrQ(ppy)(2) Complex

Authors: Ciobotaru, IC; Crisan, DN; Sket, P; Ciobotaru, CC; Polosan, S

Published: APR 2020, MATERIALS, 13, DOI: 10.3390/ma13071617

The molecular structure of the 8-hydroxyquinoline-bis (2-phenylpyridyl) iridium (IrQ(ppy)(2)) dual emitter organometallic compound is determined based on detailed 1D and 2D nuclear magnetic resonance (NMR), to identify metal-ligands coordination, isomerization and chemical yield of the desired compound. Meanwhile, the extended X-ray absorption fine structure (EXAFS) was used to determine the interatomic distances around the iridium ion. From the NMR results, this compound IrQ(ppy)(2) exhibits a trans isomerization with a distribution of coordinated N-atoms in a similar way to facial Ir(ppy)(3). The EXAFS measurements confirm the structural model of the IrQ(ppy)(2) compound where the oxygen atoms from the quinoline ligands induce the splitting of the next-nearest neighboring C in the second shell of the Ir3+ ions. The high-performance liquid chromatography (HPLC), as a part of the detailed molecular analysis, confirms the purity of the desired IrQ(ppy)(2) organometallic compound as being more than 95%, together with the progress of the chemical reactions towards the final compound. The theoretical model of the IrQ(ppy)(2), concerning the expected bond lengths, is compared with the structural model from the EXAFS and XRD measurements.

12. ZnO nanostructures grown on ITO coated glass substrate by hybrid microwave-assisted hydrothermal method

Authors: Filip, A; Musat, V; Tigau, N; Polosan, S; Pimentel, A; Ferreira, S; Gomes, D; Calmeiro, T; Martins, R; Fortunato, E

Published: APR 2020, OPTIK, 208, DOI: 10.1016/j.ijleo.2020.164372

Over the last decades, zinc oxide nanostructures (NSs) have been studied due to outstanding chemical and physical properties, able to serve a plethora of applications. The growth of NSs on different substrates coated with ITO film allow their direct implementation in various micro-/nano-devices. The microwave-assisted hydrothermal method is a new hybrid approach used for synthesis of oxide NSs due to unique advantages in energy efficiency/high reaction rate and possibility of obtaining different morphologies with size and shape-controlled, which are relevant for some applications. In this paper, we present a simple one step synthesis of ZnO 1D and 2D NSs with homogeneous distribution and orientation perpendicular to substrates covered with ITO film, using a microwave-assisted hydrothermal method. The effect of seed layer treatment on the structure, morphology and optical properties of the obtained NSs have been investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), UV/VIS/NIR and photoluminescence spectroscopy. The obtained ZnO NSs with 1D and 2D morphologies show high visible transmittance between 80-90 % and band gap energy values between 3.27 and 3.22 eV. The I-V curves and photoluminescence spectra indicate good ohmic contacts on both sides (ITO and Au-top electrodes) and highlight the effect of the thermal treatment of seed layer on the photoluminescence emission and electrical conductivity of the obtained NSs.

13. Magnetic and ferroelectric properties, crystal and magnetic structures of SrFe11.9In0.1O19

Authors: Turchenko, VA; Trukhanov, A; Trukhanov, S; Damay, F; Porcher, F; Balasoiu, M; Lupu, N; Chiriac, H; Bozzo, B; Fina, I; Waliszewski, J; Kostishyn, VG; Recko, K; Polosan, S

Published: APR 2020, PHYSICA SCRIPTA, 95, DOI: 10.1088/1402-4896/ab60fb

The structural investigations of SrFe11.9In0.1O19 compound synthesized by solid-state method have been carried by neutron diffraction method in a wide temperature range. The appearace of spontaneous polarization that coexists with ferrimagnetic ordering has been found out at room temperature in strontium hexaferrite partially substituted with In ions. In order to explaine the presence of ferroelectric properties in SrFe11.9In0.1O19 compound, its crystal structure has been refined within the framework of both centrosymmetric P6(3)/mmc (No. 194) and non-centrosymmetric P6(3)mc (No. 186) space groups. The analysis of refinement results allows to understand microscopic mechanism of appearance ferroelectric properties in strontium hexaferrites.

14. Crystal and magnetic structures, magnetic and ferroelectric properties of strontium ferrite partially substituted with in ions

Authors: Turchenko, V; Kostishyn, VG; Trukhanov, S; Damay, F; Porcher, F; Balasoiu, M; Lupu, N; Bozzo, B; Fina, I; Trukhanov, A; Waliszewski, J; Recko, K; Polosan, S

Published: APR 25 2020, JOURNAL OF ALLOYS AND COMPOUNDS, 821, DOI: 10.1016/j.jallcom.2019.153412

The influence of temperature factor to crystal structure as well as magnetic and electric properties of strontium hexaferrite partially substituted with diamagnetic indium ions has been investigated. Ferroelectric properties have been found out in SrFe11.9In0.1O19 compound that contradicts to conventional opinion, which describe its crystal structure within the framework of centrosymmetric space group P6(3)/mmc (No. 194). For determination features of the crystal structure, which are responsible for ferroelectric properties of strontium hexaferrite, have been carried out neutron diffraction measurements with high resolution in temperature range from 1.5 to 740 K. The analysis of hexaferrite structure has been executed within the framework both centrosymmetric and non-centrosymmetric space group. Values of coefficients of magneto crystalline anisotropy at 5 and 300 K and influence of ambient temperature to linear size of magnetic regions have been determined from magnetic measurements. (C) 2019 Elsevier B.V. All rights reserved.

15. Optical spectroscopy and dielectric properties of phosphate-tellurite glasses

Authors: Polosan, S; Nitescu, A; Secu, M

Published: MAR 2020, PHYSICA SCRIPTA, 95, DOI: 10.1088/1402-4896/ab5263

Tellurium metallic colloids were evidence in the phosphate tellurite glasses obtained by the melt quenching method over 1000 degrees C. The concentration and subsequent color of these glasses strongly depend on the preparation conditions due to the significant differences among the melting point of the component oxides. The presence of Te metallic colloids was evidenced by the magneto-optical measurements at different temperatures, by the shift of the emissions spectra with the excitation wavelength and the thermoluminescence spectra as a result of recombination between the hole centers, created during x-ray irradiation, with the quasi coupled electrons from the surface of the metallic colloids. The peak position in the absorption spectra of these metallic colloids was modeled based on generalized Mie light scattering theory on these metallic structures, taking into account the size and shape of colloids but also the dielectric constant of the phosphate tellurite glasses in which these colloids are embedded.

16. Organometallic Coatings for Electroluminescence Applications

Authors: Polosan, S; Ciobotaru, IC; Ciobotaru, CC

Published: MAR 2020, COATINGS, 10, DOI: 10.3390/coatings10030277

Organometallic compounds embedded in thin films are widely used for Organic Light-Emitting Diodes (OLED), but their functionalities are strongly correlated with the intrinsic properties of those films. Controlling the concentration of the organometallics in the active layers influences the OLED performances through the aggregation processes. These aggregations could lead to crystallization processes that significantly modify the efficiency of light emission in the case of electroluminescent devices. For functional devices with organometallic-based thin films, some improvements, such as the optimization of the charge injection, are needed to increase the light output. One dual emitter IrQ(ppy)2 organometallic compound was chosen for the aggregation correlations from a multitude of macromolecular organometallics that exist on the market for OLED applications. The choice of additional layers like conductive polymers or small molecules as host for the active layer may significantly influence the performances of the OLED based on the IrQ(ppy)2 organometallic compound. The use of the CBP small molecule layer may lead to an increase in the electroluminescence versus the applied voltage.

17. Sol-Gel Processing of Bismuth Germanate Thin-Films

Authors: Secu, M; Secu, CE; Tite, T; Polosan, S

Published: MAR 2020, COATINGS, 10, DOI: 10.3390/coatings10030255

This study aims to obtain uniform and homogeneous bismuth germanate oxides thin films by spin coating and using the sol-gel technique with different precursors, followed by low-temperature annealing at 560 degrees C. By using Bi(NO3)(3) precursors, we have obtained transparent, yellowish thin films with a 200 nm thickness. The structural analysis of the initial sol-gel powder has shown the presence of two crystalline structures, the cubic Bi4Ge3O12 (BGO) and monoclinic Bi2GeO5 crystallites, which evolves towards the BGO structure after annealing. The elemental analysis confirmed the composition of the desired compound Bi4Ge3O12 with 60 wt % GeO2 and 40 wt % Bi2O5. On the other hand, by changing the precursor to (Bi(CH3COO)(2), the film thickness increased to 500 nm thicker due to the high viscosity of the sol, and a dominant monoclinic Bi2GeO5 crystalline structure appeared. The elemental analysis revealed a nonstoichiometric composition with 38 wt % GeO2 and 62 wt % Bi2O3. Due to the low GeO2 phase content that reacted with metastable Bi2GeO5, we obtained cubic Bi4Ge3O12 as a secondary phase, with Bi2GeO5 as a dominant crystalline phase. The redshifts of both absorptions and emissions spectra peaks confirmed a different disorder structure as an interplay between the cubic Bi4Ge3O12 (BGO) and monoclinic Bi2GeO5 phases.

18. Charge Transfer from Alq(3)-5Cl to Graphene Oxide in Donor-Acceptor Heterostructures

Authors: Polosan, S; Ciobotaru, CC; Ciobotaru, IC

Published: NOV 2019, JOURNAL OF ELECTRONIC MATERIALS, 48, DOI: 10.1007/s11664-019-07531-w

This paper describes an alternative active layer for the solar cells based on the organometallic compounds in two configurations: bulk heterojunction and donor/acceptor junction between the organometallic compounds as the electron donor and carbon-based layer as the electron acceptor. Both configurations depend on the band alignment which ensures optimal charge transport towards electrodes in the sandwich structures of these active layers, but the optimization also depends by the exciton diffusion length which limits the thicknesses of the active layer. In the bulk heterojunctions, the exciton diffusion length could be extended to 100 nm which allows a better efficiency then bilayer structures. The photoconductive behaviors of these two configurations have shown the superiority of the bulk heterojunctions, increasing the intensity of the measured photocurrent. The redshift of the photoluminescence of Alq3-5Cl in the bulk heterojunctions reveals a better charge transfer towards the acceptor layer, in this case, formed from graphene oxide. The alternative of organometallic compounds as donor materials ensures a better thermal and chemical stability compared with other organic materials like perovskites.

19. Efficiency enhancement of iridium-based organometallic light emitting diodes

Authors: Polosan, S

Published: MAY 2019, MATERIALS RESEARCH EXPRESS, 6, DOI: 10.1088/2053-1591/ab0625

The efficiency of the Organic Light Emitting Diode (OLED) is given either by the internal quantum efficiency of the organometallic compound or by the charge transport across OLED. IrQ(ppy)(2) is a new organometallic compound which gives green and red electroluminescence. This dual emitter compound exhibits a lower internal quantum efficiency compared with classical Ir(ppy)(3) green emitter because of a weak coupling between Ir3+ and oxygen ions which significantly reduces the charge transfer towards quinoline ligand. This lower internal quantum efficiency is compensated by the higher electron donor character of the quinoline ligand which induces better change transport in OLED structures. In the case of Ir(ppy)(3) green emitter, the efficiency can be improved by adding magnetic or metallic nanoparticles which significantly change the charge transport for the Ir(ppy)(3) based OLED structures. The metallic or magnetic nanoparticles embedded in the transparent and conductive polymer, reduce the electron injection, acting as filling traps, which directly increases the electroluminescence and the current at the same voltage.

20. Structure and low field magnetic properties in phosphate-tellurite glasses

Authors: Polosan, S

Published: NOV 15 2019, JOURNAL OF NON-CRYSTALLINE SOLIDS, 524, DOI: 10.1016/j.jnoncryso1.2019.119651

Phosphate-tellurite glasses exhibit magnetic properties, due to the presence of the small metallic Te colloids which were revealed in low field magnetic circular dichroism. These metallic colloids induce the red coloring of these glasses together with the absorbance in the visible region. The temperature dependence of the absorption spectrurn and the A-term in magnetic circular dichroism are specific for Te metallic nanoparticles, which results during the melting procedure over 1000 degrees C due to the conversion of Te4+ in Te-0 atoms. The X-ray photoelectron spectroscopy supports this fact due to the presence of small peaks as satellites in the region of Te 3d core-level spectrum. Quantification of these satellites compared with Te 3d(3/2) and 3d(5/2) peaks suggests a 14% concentration of Te metallic nanoparticles in these phosphate-tellurite glasses. The presence of metallic particles induces the crystallization effects of Te micrograins upon thermal treatments at higher temperatures.

21. Crystallization processes in europium-doped Bi4Ge3O12 glass materials

Authors: Polosan, S

Published: SEP 2019, JOURNAL OF LUMINESCENCE, 213, 240, DOI: 10.1016/j.jlumin.2019.05.031

Crystallization processes of bismuth germanate glasses may be evidenced by the optical properties of Eu3+ ions, used as probes because these ions substitute the Bi3+ ions in the glass-ceramic samples. The gradual thermal annealing of these glasses induces rearranging of GeO4 tetrahedra around Bi3+ ions and transforms the red colored glasses in transparent glass-ceramic samples. The red color comes from the light scattering on GeO4 clusters and, after rearranging in Bi4Ge3O12 nanoparticles, convert the glass-ceramic samples in transparent materials. One of the most essential information is given by the phonon side bands investigations which, coupled with the Raman spectra allows the identification of Bi4Ge3O12 lattice vibration but also those of residual GeO4 tetrahedra. The measurements of the luminance and CIE circle have shown a significant increase of the light emission for the glass-ceramic samples, while the Magnetic Circular Dichroism indicate lower symmetry coordination around the Eu3+ ions in the glass sample compared with the glass-ceramic and also a change in the coordination number to the higher values.

22. Organometallic compounds for photovoltaic applications

Authors: Ciobotaru, IC; Polosan, S; Ciobotaru, CC

Published: NOV 1 2018, INORGANICA CHIMICA ACTA, 483, 453, DOI: 10.1016/j.ica.2018.08.042

Organometallic compounds could be an excellent alternative to the organic active layers for solar cells due to several better properties like thermal and chemical stability. These organometallic compounds are electron donor materials which are easily used in donor-acceptor heterojunctions in these solar cells. One of the main problems for the active media in the solar cells is connected with the exciton diffusion length which limits the thickness of the donor layer in these donor-acceptor heterojunctions. A way to improve the exciton diffusion length is better charge transfer between the donor and acceptor facilitating the exciton diffusion towards the electrodes of the solar cells. The adding of electronegative ions or chemical groups could also influence the band alignment between the donor and acceptor smoothing the charge transport across the solar cells.

23. Charge carrier traps in tris-(8-hydroxyquinoline) aluminum

Authors: Secu, M; Polosan, S

Published: FEB 2018, JOURNAL OF LUMINESCENCE, 194, 95, DOI: 10.1016/j.jlumin.2017.10.003

Thermoluminescent measurements between 40 and 300 C revealed two traps in the irradiated Alq(3) powder synthetized from Al(OH)(3), at 0.8 and 1.1 eV below the conduction band. These two traps have been assigned with the Alq(3) facial and meridional isomers and the trapping process stand for a long time after the switching off the irradiation source. The spectra recorded an hour after switching recover 60% from the photoluminescence and also decreasing the TL signals. A theoretical model was proposed in order to explain the trapping and detrapping processes in both meridional and facial Alq(3) isomers based on the XPS measurements for the HOMO, LUMO, ionization potential and optical bandgap, completed with the DFT calculated parameters and similar experimental results concerning the evidences of the triplet states in Alq(3) compound.

24. Electroluminescence Properties of IrQ(ppy)(2) Dual-Emitter Organometallic Compound in Organic Light-Emitting Devices

Authors: Ciobotaru, CC; Polosan, S; Ciobotaru, IC

Published: FEB 2018, JOURNAL OF ELECTRONIC MATERIALS, 47, 1496, DOI: 10.1007/s11664-017-5945-3

This paper reports the influence of the charge carrier mobility on the electroluminescent properties of a dual-emitter organometallic compound dispersed in two conjugated organic small-molecule host materials and embedded in organic light-emitting devices (OLEDs). The electroluminescent processes in OLEDs are strongly influenced by the host-guest interaction. The charge carrier mobility in the host material plays an important role in the electroluminescent processes but also depends on the triplet-triplet interaction with the organometallic compound. The low charge carrier mobility in 4,4'-bis(N-carbazolyl)-1,1'-biphenyl (CBP) host material reduces the electroluminescent processes, but they are slightly enhanced by the triplet-triplet exothermic charge transfer. The higher charge carrier mobility in the case of N, N'-bis(3-methylphenyl)-N, N'-diphenylbenzidine (TPD) host material influences the electroluminescent processes by the endothermic energy transfer at room temperature, which facilitates the triplet-triplet harvesting in the host-guest system. The excitation is transferred to the guest molecules by triplet-triplet interaction as a Dexter transfer, which occurs by endothermic transfer from the triplet exciton in the host to the triplet exciton in the guest.

25. Low energy electron irradiation of carbon thin films

Authors: Pacala, O; Ciuca, I; Logofatu, C; Polosan, S

Published: MAY 2018, MATERIALS RESEARCH EXPRESS, 5, DOI: 10.1088/2053-1591/aac472

Low energy electrons irradiation represent an alternative method for the chemical and thermal treatments used in the elimination of sp(3) hybridization of carbon thin films and restoring the sp(2) structures. The procedure significantly reduces the added chemical groups mainly hydroxyl ones presented in alcohols, on the surfaces of the carbon deposited thin films. Irradiation induces a graphitization process of deposited carbon thin films revealed by the x-ray diffraction, x-ray photoelectrons spectroscopy, Raman spectroscopy and sheet resistance measurements which demonstrate a gradual elimination of the add-on chemical groups together with the increasing of electrical conductivity in these carbon films.

26. Crystallisation of bismuth germanate glasses below their glass transition temperature

Authors: Polosan, S

Published: SEP 15 2017, JOURNAL OF NON-CRYSTALLINE SOLIDS, 472, 60, DOI: 10.1016/j.jnoncrysol.2017.07.010

Dielectric measurements of bismuth germanate oxides reveal significant changes in the amorphous phase, between 200 and 350 degrees C, where the crystallisation processes start below the glass transition temperature. The capacitive and loss measurements versus temperature and frequency suggest an incipient glass transition below 350 degrees C associated with an increase in the clusters, mainly those formed by GeO4 tetrahedra, responsible for the dipolar orientation effects. An increase in the capacitive parameter versus temperature at lower frequencies, especially over 250 degrees C has been associated with the increase in mobility of the clusters. The physical meaning of those processes has been associated with the formation of a highly viscous layer enriched in GeO4 which is formed during crystallisation. This layer acts as a diffusion barrier and hinders further crystal growth. A higher frequency is required in the crystallisation processes to compensate for the thermal disorder in the amorphous materials. The crystallisation process is identified by the decrease in the dielectric constant despite the increase in temperature.

27. Crystallization properties of IrQ(ppy)(2) organometallic complex films

Authors: Polosan, S; Ciobotaru, CC; Ciobotaru, IC; Tsuboi, T

Published: MAY 2017, JOURNAL OF MATERIALS RESEARCH, 32, 1740, DOI: 10.1557/jmr.2017.155

Comparative studies between doped conducting polymers and electrochemical deposited organometallic compounds reveals the interplay between crystalline-amorphous phases with significant contributions to the internal quantum efficiency in the OLED devices. The coexistence of the amorphous and crystalline phase in the electrodeposited film is revealed by the minor micro-crystal products which are present in the amorphous phase in thin films, while the many micro-crystals are randomly distributed in the thick films. Concerning the doped conducting polymers, the level of doping induces crystalline effects as a result of the - stacking between molecules, due to the Forester energy transfer processes in which the transfer rate is increased with decreasing of the distances between neighboring molecules. The crystallization processes change the emission properties of the active layers both for the luminance level and all over color, ranging from yellow to red in the case of IrQ(ppy)(2) compounds.

28. Enhancement of the electroluminescence of organic light emitting devices based on Ir(ppy)(3) by doping with metallic and magnetic nanoparticles

Authors: Ciobotaru, CC; Ciobotaru, IC; Schinteie, G; Negrea, R; Polosan, S

Published: DEC 2017, MATERIALS SCIENCE IN SEMICONDUCTOR PROCESSING, 72, 84, DOI: 10.1016/j.mssp.2017.09.019

Magnetic nanoparticles embedded in the active layer of the Organic Light Emitting Diodes (OLEDs) significantly increases the electroluminescence and the charge transport without influencing the transparency of these devices. A brief comparison was done in order to identify which parameter influences these properties, by comparing the CoFe2O4 magnetic nanoparticles with CoFe2 metallic magnetic nanoparticles, the latter one being obtained by thermal reduction in hydrogen of cobalt ferrite nanoparticles. CoFe2 have shown a better efficiency of the metallic nanoparticles where probably the main advantage is the higher magnetization property instead of the coercive field. Concerning the charge transport across the OLEDs, these nanoparticles reduce the electron injection, acting as filling traps, which directly increases the electroluminescence and the current at the same voltage.

29. Templateless electrodeposition ZnO nanowires for charge transport optimization in OLED structures

Authors: Polosan, S; Matei, E; Ciobotaru, IC; Ciobotaru, CC

Published: OCT 2016, MATERIALS RESEARCH EXPRESS, 3, DOI: 10.1088/2053-1591/3/10/105018

Passivated zinc oxide nanowires (NW) were used to improve the charge injection in organic lightemitting diode (OLED) structures. Conducting polymers, deposited on the well-dispersed ZnO NW, were used to modify the electrical conductivity across the OLED structure because the charge transport is influenced by the interface interactions. Passivation with polymers improves the transport characteristics of the device due to the interaction between ZnONWand PEDOT:PSS polymer. The hole current density increases with the ZnO NW concentration, which made the current injection more balanced and therefore enhanced the electroluminescence efficiency. A templateless electrochemical deposition method was used to grow zinc oxide nanowires on an ITO/glass substrate because parameters such as the densities and dimensions of the nanowires can be controlled to produce thin and well dispersed structures.

30. STRUCTURAL AND MORPHOLOGICAL EVOLUTIONS INDUCED BY THE ANNEALING OF CaF2 NANOCRYSTALLINE POWDERS BY USING Eu3+ ION PROBE LUMINESCENCE

Authors: Polosan, S; Secu, M; Enculescu, M

Published: APR-JUN 2016, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 11, 624, DOI:

Eu-doped CaF(2)nanocrystalline powders have been prepared by using co-precipitation technique. Structural and morphological modifications induced by annealing are followed by using Eu3+-ion probe. Theluminescence properties are changing gradually together with the morphology of doped CaF2 nanoparticles accompanied by anEu(3+)-> Eu2+ conversion. Cathodoluminescence measurements show uniform distribution of the europium dopant ions in the annealed samples accompanied by a strong increase of the integral photoluminescence signal. During annealing the cubic structure of CaF2 nanoparticles is altered going to the spherical morphology due to the Eu3+ ions incorporation. In the annealed samples Eu3+ ions are incorporated as Eu3+-O dimer centres with the coordination symmetry (C-2 nu); in the sintered samples there are two non-equivalent Eu3+ sites. The thermoluminescence peaks have been assigned to the recombination of the Eu3+ related traps in these sites.

31. Ferromagnetic behaviour of bismuth germanate oxides glass-ceramic materials

Authors: Polosan, S; Negrea, R; Ciobotaru, IC; Schinteie, G; Kuncser, V

Published: FEB 25 2015, JOURNAL OF ALLOYS AND COMPOUNDS, 623, 196, DOI: 10.1016/j.jallcom.2014.10.104

The content of defects in Bi4Ge3O12 (BGO) glass-ceramic materials together with their ordering during crystallization induces ferromagnetic behaviours in these materials. The observed ferromagnetism has to be associated strictly with the GeO4 related defects in the atypical amorphous phase. The photoluminescence of BGO glass-ceramic materials can give useful information about the nature of defects, especially the oxygen vacancies from the GeO4 tetrahedra and Bi4Ge3O12 cubic structures. The concentration of these defects depends on annealing between 600 degrees C and 700 degrees C where orthorhombic and cubic phases coexist. The magnetization at saturation is higher in the samples dominated by the amorphous phase and the strength of the exchange interaction is higher in the samples dominated by the cubic phase, obtained over 700 degrees C, when the GeO4 tetrahedra are rearranged during crystallization together with their oxygen vacancies. (C) 2014 Elsevier B.V. All rights reserved.

32. Absorption, phosphorescence and Raman spectra of IrQ(ppy)(2) organometallic compound

Authors: Polosan, S; Ciobotaru, IC; Tsuboi, T

Published: JUL 15 2015, MATERIALS CHEMISTRY AND PHYSICS, 162, 830, DOI: 10.1016/j.matchemphys.2015.07.009

The absorption and photoluminescence (PL) spectra, PL decays, Raman spectrum, cyclic voltammetry (CV) and nuclear magnetic resonance of heteroleptic Ir-compound IrQ(ppy)(2) compound with two phenylpyridine (ppy) ligands and one quinoline (Q) ligand have been investigated experimentally and theoretically. Two very weak absorption bands due to the transitions to the triplet states are found at about 560 and 595 nm in IrQ(ppy)(2) doped in CH2Cl2 solution. IrQ(ppy)(2) exhibits a dual emission of red and green phosphorescence bands. The red emission intensity is much higher than the green one in IrQ(ppy)(2) powder, but much lower than the green one in lightly IrQ(ppy)(2)-doped CH2Cl2 solution and PMMA film. The intensity ratio of the red emission to the green emission, however, is observed to increase with increasing the IrQ(ppy)(2) concentration in CH2Cl2 solution and PMMA film. The enhancement of the red emission is suggested to be caused by the Forester energy transfer from Ir-ppy component to Ir-Q components between two neighboring IrQ(ppy)(2) molecules. The HOMO energy is estimated to be -4.865 eV from the CV measurement, which is close to the HOMO energy of -4.844 eV calculated using the time dependent density function theory (TD-DFT). The LUMO energy is estimated as -2.856 eV from the HOMO energy and the long-wavelength absorption edge found at 617 nm in the absorption spectrum. The absorption spectrum of IrQ(ppy)(2) is calculated by the TD-DFT. Discussion is given on a deviation of the calculated spectrum from the measured spectrum. (C) 2015 Elsevier B.V. All rights reserved.

33. Conformational changes and metastable states induced in proteins by green light

Authors: Comorosan, S; Popescu, I; Polosan, S; Pirvu, C; Ionescu, E; Paslaru, L; Apostol, M

Published: JAN 8 2015, EUROPEAN PHYSICAL JOURNAL B, 88, DOI: 10.1140/epjb/e2014-50717-8

In this paper we report conformational changes recorded on a protein molecule (alpha-amylase) under green light irradiation. In order to explain the experimental results we advanced the hypothesis that green light induces electric dipoles in the protein, which interact with each other, generating conformational modifications toward a more compact design, with different physical properties. The experiments were carried out with un-polarized light (lambda = 520 nm) from a light-emitting-diode (1000 lm, 20 W, 105 mW on the target). In view of the character of our hypothesis, and corroborated with all our experimental results, we suggest that this phenomenon may be more extended and general, specific for a larger class of proteins, occurring on the protein macromolecules under the green light. The effects of a-amylase protein irradiation were revealed by circular dichroism, fluorescence, Raman and FTIR-spectroscopies, zeta potential, cyclic voltammetry, electric impedance spectroscopy and atomic force microscopy. Tentatively, we term the novel conformations as P* (polarized) proteins.

34. Thermally activated conversion of a silicate gel to an oxyfluoride glass ceramic: Optical study using Eu3+ probe ion

Authors: Secu, CE; Bartha, C; Polosan, S; Secu, M

Published: FEB 2014, JOURNAL OF LUMINESCENCE, 146, 543, DOI: 10.1016/j.jlumin.2013.10.013

Sol-gel route using metal alkoxides precursor and trifluoroacetic acid as in situ fluorination reagent has been used to prepare Eu3+ -doped silicate xerogel, followed by thermal annealing to obtain oxyfluoride glass ceramic containing Eu3+ -doped BaF2 nanocrystals. We have used Eu3+ as probe ion and we analyzed its characteristic features (photoluminescence, optical absorption and magnetic circular dichroism) to get information about the local environment around the ion during thermally activated evolution of the sol to xerogel and then glass ceramic. As the drying and annealing proceeds silica network is formed accompanied by precipitation of the nanofluoride crystalline phase; Eu3+ coordination changes gradually from a random and assymetric CF3COO- one (in the sol) to a symmetric one (in the BaF2 nanocrystals) given by the fluorine ions. Glass ceramization is based on a homogenous crystallization mechanism with BaF2 nucleation centres resulted from thermal decomposition of Ba-trifluoacetate at around 300 degrees C followed by subsequent growth into BaF2 nanocrystals above 600 degrees C; Eu3+-ions are incorporated during the nanocrystals growth. (C) 2013 Elsevier B.V. All rights reserved.

35. Structural characteristics of iridium dual-emitter organometallic compound

Authors: Polosan, S; Ciobotaru, IC; Enculescu, I; Ciobotaru, CC

Published: DEC 14 2014, JOURNAL OF MATERIALS RESEARCH, 29, 2904, DOI: 10.1557/jmr.2014.337

By combining two types of ligands, phenylpyridine and quinoline, a new type of organometallic IrQ(ppy)(2) compound has been synthesized, which exhibits two phosphorescences: green and red. Using an appropriate catalyst, the final IrQ(ppy)(2) compound has a good chemical yield up to 60% and becomes a stable dual emitter at room temperature. This compound is important because it exhibits stable red emission which is limited by the quantum yield due to the low energy band gap. As a result, an overlap between the ground state and the excited state occurs due to the vibrations that increase the nonradiative transitions, destroying the red emissions. Structural characteristics of the IrQ(ppy)(2) powder reveal a triclinic structure confirmed by x-ray diffraction and scanning electron microscopy images. Thermal analysis of the final compound confirms a good stability against decomposition and structural changes up to 350 degrees C. X-ray photoelectron spectroscopy reveals Ir-O chemical bonds and several differences between the intermediate and final compounds, such as Ir-Cl bonds. Cathodoluminescence patterns show a phosphorescent triclinic structure with a higher efficiency for the red color. Backscattering electron images prove that there is a uniform distribution of iridium ions in the IrQ(ppy)(2) nanocrystals.

36. COVALENT FUNCTIONALIZATION OF SINGLE WALLED CARBON NANOTUBES WITH DOXORUBICIN FOR CONTROLLED DRUG DELIVERY SYSTEMS

Authors: Ciobotaru, CC; Damian, CM; Polosan, S; Matei, E; Iovu, H

Published: JAN-MAR 2014, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 9, 422, DOI:

The objective of this study was to obtain nanocomposites based on SWCNTs functionalized with carboxyl groups and doxorubicin (DOX) as a chemotherapeutic drug through covalent bonds formed by carboxyl groups from SWCNTs and amino groups from DOX. The formation of these nanocomposites was proved by using different characterization methods like Fourier transform Infrared spectroscopy and X-ray photoelectron spectroscopy (XPS). Also thermogravimetrical analysis was employed to study the thermal behavior of our nanocomposites. X-ray diffraction and Raman spectroscopy revealed that the surface was modified by the covalent bonding of DOX to SWCNTs. The in vitro drug release was studied by using UV-VIS Spectroscopy.

37. DRUG DELIVERY STUDY OF SINGLE-WALL CARBON NANOTUBES COVALENT FUNCTIONALIZED WITH CISPLATIN

Authors: Ciobotaru, CC; Damian, CM; Polosan, S; Prodana, M; Iovu, H

Published: APR-JUN 2014, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 9, 868, DOI:

Carbon nanotubes are widely studied components for drug delivery systems due to their high surface area and low chemical reactivity. The research presented in this paper deals with the synthesis of drug delivery systems based on single walled carbon nanotubes (SWCNTs) and the well-known cancer treatment drug Cisplatin. The new nanomaterials obtained through covalent bonding between carboxyl groups from the SWCNTs surface and amino groups from the Cisplatin structure were characterized from structural point of view. To evaluate the content of drug released the Inductively Coupled Plasma Mass Spectrometry (ICP-MS) was employed. The releasing profile shows a slow rate in the beginning followed by a spectacular increase after 180 minutes which means that this type of system could be used for prolonged release.

38. Embedding of IrQ(ppy)(2) organometallic compounds in polypyrrole conducting polymer for OLED's applications

Authors: Ciobotaru, IC; Matei, E; Ciobotaru, CC; Polosan, S

Published: DEC 2014, SYNTHETIC METALS, 198, 328, DOI: 10.1016/j.synthmet.2014.10.041

Conducting polypyrrole:IrQ(ppy)(2) thin films were obtained by electrochemical method which ensure uniform dispersion of the organometallic in the polymer matrix. A thin layer of about 50 nm polypyrrole: IrQ(pPY)(2) thin films were deposited on the ITO/glass substrate and used for spectroscopic, structural, and electric characterization. The photoluminescence spectrum of polypyrrole:IrQ.(ppy)2 have shown the two main emissions of IrQ(ppy)(2) at 2.44 eV (508 nm) and 2 eV (620 nm) besides of the polypyrrole weak emission centered at 2.55 eV (485 nm). The electric conductivity of the doped polypyrrole thin layer has almost the same conductivity with the undoped polypyrrole thin film suggesting an homogenous polypyrrole:IrQ(ppy)(2) composite which can be used as emissive layer in the OLED's structures. (C) 2014 Elsevier B.V. All rights reserved.

39. Dual emitter IrQ(ppy)(2) for OLED applications: Synthesis and spectroscopic analysis

Authors: Ciobotaru, IC; Polosan, S; Ciobotaru, CC

Published: JAN 2014, JOURNAL OF LUMINESCENCE, 145, 262, DOI: 10.1016/j.jlumin.2013.07.067

The synthesis of organometallic compound with iridium and two types of ligands, quinoline and phenylpyridine, was done successfully. The absorption spectra of this compound have shown broad peaks in a visible region assigned to metal-to-ligands charge transfer and in UV region assigned to intraligand absorptions. The photoluminescence spectra exhibit dual character in which the red emission is more intense than the green one. In cathodoluminescence measurements, under electron beam, the powder obtained after recrystallization from dichloromethane, shows similar behaviors with photoluminescence spectra. The cathodoluminescence images have shown a luminescent crystalline powder with triclinic structure. This compound exhibits combined vibrational modes, which proves the presence in the same molecule of both ligands. Density Functional Theory calculation was involved in order to identify the main vibrations of this compound. (C) 2013 Elsevier B.V. All rights reserved.

40. Mechanisms of the Charge Transfer in IrQ(ppy)(2)-5Cl Dual-Emitter Compound

Authors: Polosan, S; Radu, IC

Published: JUL 2013, JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 13, 5208, DOI: 10.1166/jnn.2013.7513

The synthesis of IrQ(ppy)(2)-5Cl has the advantage of a dual phosphorescence (green and red) which comes from the two ligands, phenylpyridine and quinoline. Their spectroscopic properties evidences the absorption range between 350 nm to 700 nm which is composed from the singlet and triplet states, as a result of hybridizations between Ir and the two ligands, the first one being at 625 nm. The first low energy state comes from the quinoline ligand and is responsible for the red phosphorescence at 660 nm, as results from the Density Functional Theory (DFT) analysis. The hybridization between Ir 5d orbitals and pi ligand orbitals shows strong metallic character with phenylpyridine orbitals (66% and 43%) and weak metallic character with quinoline ligand (16.8%). This fact suggests weak phosphorescence intensity in the emission spectra. Population analysis of each metallic orbital shows a small charge delocalization on the quinoline ligand for the first molecular orbital and a strong delocalization on the phenylpyridine ligands. Solvation effects induce a tuning process for the phosphorescence by changing of the matrix of the organometallic compounds which can be adjusted by the strength of intermolecular dipole-dipole interactions, using a doped guest-host molecular organic thin film system.

41. Optical manipulation of complex molecular systems by high density green photons: experimental and theoretical evidence

Authors: Comorosan, S; Polosan, S; Popescu, I; Stamatin, I; Ionescu, E; Avramescu, S; Cune, LC; Apostol, M

Published: MAY 2013, EUROPEAN PHYSICAL JOURNAL B, 86, DOI: 10.1140/epjb/e2013-40049-8

The recent revolution in modern optical techniques revealed that light interaction with matter generates a force, known as optical force, which produces material properties known in physics as optical matter. The basic technique of the domain uses forces exerted by a strongly focused beam of light to trap small objects and subsequently to manipulate their local structures. The purpose of this paper is to develop an alternative approach, using irradiations with high-density-green-photons, which induce electric dipoles by polarization effects. The materials used for the experiments were long carbon chains which represent the framework of biological macromolecules. The physical techniques used to reveal the locally induced molecular arrangements were: dynamic viscosity, zeta potential, chemiluminescence, liquid chromatography; mass spectrometry, and Raman and infrared spectroscopy. The principal result of our experiments was the detection of different molecular arrangements within the mixture of alkane chains, generated by our optical manipulations. This induced "optical matter" displayed two material properties: antioxidant effects and large molecular aggregation effects. In order to bring the experimental results in relation with theory, we developed a physical model and the interacting force between polarizable bodies was computed. By numerical calculations stable structures for N = 6 and N = 8 particles were obtained.

42. Lead incorporation mechanism in LiF crystals

Authors: D'Acapito, F; Pochet, P; Somma, F; Aloe, P; Montereali, RM; Vincenti, MA; Polosan, S

Published: FEB 25 2013, APPLIED PHYSICS LETTERS, 102, DOI: 10.1063/1.4793751

The doping process of LiF with Pb has been described by using structural ab initio modeling and experimental results. The values of formation energy of several complexes involving Pb ions show that the presence of charge-balancing vacancies ease the metal incorporation in the crystal. The metal successively captures the vacancies to form a final stable complex Pb-Li(center dot) + V-Li('). Experimental data from X-ray absorption spectroscopy confirm the presence of Pb in LiF crystals in this site revealing both Pb-F bonds and collinear Pb-F-Li atomic configurations. A maximum solubility of Pb in LiF of the order of 3 x 10(20)/cm(3) can be estimated from these calculations. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4793751]

43. Antioxidant effects induced in biological macromolecular systems by high density photons through localized excitations

Authors: Comorosan, S; Polosan, S; Popescu, I; Paslaru, L; Nastase, A; Mitrica, R; Ionescu, E

Published: OCT 2012, BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS, 1817, S130, DOI: 10.1016/j.bbabio.2012.06.345

44. Cathodoluminescence and Raman analysis of the finite-size effects in mer-Alq(3) structure

Authors: Radu, IC; Polosan, S; Enculescu, I; Iovu, H

Published: DEC 2012, OPTICAL MATERIALS, 35, 273, DOI: 10.1016/j.optmat.2012.08.017

As synthesized mer-Alq(3) powder, obtained by wet chemical synthesis, has been subjected to different new characterization techniques such as Energy Dispersive X-ray, Cathodoluminescence and Scanning Electron Microscopy in order to identify their structural and photophysical properties. Other common techniques like X-ray diffraction, Raman and Fourier Transform Infrared spectroscopy have been involved in order to prove the formation of mer-Alq(3) compound. The vibrational spectroscopic properties were interpreted by using the output files from Gaussian software with B3YLP functionals and 6-311(d) basic sets. The growth kinetic of mer-Alq(3) nanocrystals in the alpha-phase has been evaluated by using the finite-size effects based on the Raman position peaks and their linewidths, which confirms the semiconductor character of the mer-Alq(3) compound. The XRD results suggest that the isothermal annealing increases the mer-Alq(3) nanocrystals, which modify the regular shape of typical spectral parameters from Raman peaks. (C) 2012 Elsevier B.V. All rights reserved.

45. HIGH-DENSITY GREEN PHOTONS EFFECTS ON NaCl SOLUTIONS DETECTED BY RED BLOOD CELLS MEMBRANES

Authors: Mitrica, R; Popescu, I; Paslaru, L; Badila, D; Polosan, S; Cristache, L; Ionescu, E; Tataru, C; Comorosan, S

Published: JAN-MAR 2012, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 7, 235, DOI:

This paper presents a new technique for investigating the modifications induced by high-density green light [GL] on water in NaCl solutions. Solutions of 0,45 g% and 0,9 g%, irradiated with green light (lambda = 527 nm, intensity 3.10(5) Lx) were used. As a receptor for measuring the irradiation effect we used red blood cell (RBC) permeability in hypotonic media, the so-called osmotic shock. After RBC lysis in hypotonic medium, the released hemoglobin was spectrophotometrically determined at lambda = 550 nm. The values of the osmotic shock for the samples obtained with GL-irradiated NaCl solutions were significantly lower than the values obtained with non-irradiated controls. This may indicate that the penetration of water inside the membranes canaliculi is hindered. This new type of result was complemented by chronoamperometry and impedance spectroscopy determinations. The current density of the irradiated solution decreases from the value of 29.5 mu A.cm(-2) in the control to 17.74 mu A.cm(-2) in the irradiated sample with a corresponding decrease of ionic mobility. The impedance value of the GL irradiated NaCl solutions were significantly lower than the control values, thus correlating well with the data recorded by chronoamperometry. All these data may indicate large water cluster formation through GL irradiation which are beyond the cellular aquaporine channels capacity. A similar process is identified by using red light, as well as blue light, though with a much smaller output.

46. Photoluminescence and magnetic circular dichroism of IrQ(ppy)(2)-5Cl

Authors: Polosan, S; Radu, IC; Tsuboi, T

Published: APR 2012, JOURNAL OF LUMINESCENCE, 132, 1002, DOI: 10.1016/j.jlumin.2011.12.002

Photoluminescence and magnetic circular dichroism of the IrQ(ppy)(2)-5Cl compound were investigated between 15 and 295 K. These results have been compared with the output files obtained from Density Functional Theory by using the Gaussian 03W software and some additional packages. The experimental results confirm the first triplet state absorption which arises from d to pi(Q) transition. The temperature dependence photoluminescence have shown a small interaction with the polystyrene, used for dispersion of IrQ(ppy)(2)-5Cl compound. The green and red phosphorescence have the same temperature dependence. The MCD spectra, especially at 15K, reveals the main transitions involved in the Metal-to-Ligand Charge Transfer processes from the Ir towards the two ligands, phenylpyridine and quinoline, respectively. (C) 2011 Elsevier B.V. All rights reserved.

47. Investigations of the non-isothermal crystallization of Bi4Ge3O12 (2:3) glasses

Authors: Aldica, G; Polosan, S

Published: MAY 1 2012, JOURNAL OF NON-CRYSTALLINE SOLIDS, 358, 1227, DOI: 10.1016/j.jnoncrysol.2012.02.025

Amorphous Bi4Ge3O12 glass samples were produced by melt quenching procedure stating with Bi4Ge3O12 (BGO) powder, obtained by solid state reaction between oxides. The kinetics of non-isothermal crystallization of EGO nano-crystals has been investigated. Differential Thermal Analysis (DTA) can give the main parameters of crystallization with an exothermic peak from 813 K to 851 K depending on the heating rate, which was assigned to the crystallization of cubic BGO in the amorphous matrix and compared with the X-Ray Diffraction (XRD) patterns. The nano-crystal dimensions were calculated from the XRD patterns by using the Debye-Scherrer method and were compared with Transmission Electron Microscopy (TEM) images. It was shown that the Ozawa model is most suitable for describing the behavior of non-isothermal crystallization of EGO nano-crystals within the glass matrix. Experimental results suggest a disk-shape type growth mechanism for the Bi4Ge3O12 nano-crystallites. The Flynn-Wall-Ozawa method has shown that the average activated energy value is 385 +/- 14 kJ/mol which was computed within the same model and agrees very well with the activation energy of the crystallization. (C) 2012 Elsevier B.V. All rights reserved.

48. Magneto-optical investigations of rare earth doped sol-gel derived silicate xerogels

Authors: Secu, CE; Polosan, S; Secu, M

Published: AUG 2011, JOURNAL OF LUMINESCENCE, 131, 1752, DOI: 10.1016/j.jlumin.2011.04.031

Rare-earth doped xerogels (Eu3+, Sm3+, Ho3+, Pr3+) were prepared by using the sal-gel method and their magneto-optical and optical properties have been studied. The Magnetic Circular Dichroism (MCD) spectra are quite similar to those recorded in the RE-doped fluorozirconate glasses; the fine structures shown by the MCD spectra are better resolved compared to the optical absorption spectra. The MCD technique has been correlated with optical measurements in order to investigate the site symmetry in the particular case of Eu3+-doped xerogel and oxyfluoride glasses. In the xerogel, coordination symmetry around the Eu3+ ions is close to (D) under bar (3h) and is lower in the oxyfluoride glass. (C) 2011 Elsevier B.V. All rights reserved.

49. Band-gap correlations in Bi4Ge3O12 amorphous and glass-ceramic materials

Authors: Polosan, S; Galca, AC; Secu, M

Published: JAN 2011, SOLID STATE SCIENCES, 13, 53, DOI: 10.1016/j.solidstatesciences.2010.10.007

The Bi4Ge3O12 (BGO) glass materials were sintered from a mixture of oxides powders, rapidly heated and melted at 1323 K and poured on the graphite plates heated at different temperatures. Their optical properties are compared with BGO single crystals being strongly dependent by the experimental conditions, which influence the further stability of the samples. The dielectric functions of the samples reveal a clear difference between the two phases (amorphous and crystalline). The refractive index of the amorphous phase has lower values which indicate that the density of the material is diminishes. Also, a sign of disorder is seen in optical absorption (extinction coefficient). From the optical band gap determinations of those two phases, it is confirmed the disorder structure and red-shifts of the band gap value compared with crystalline phase. The absorption spectra are in good agreement with the ellipsometric measurements, regarding the transparency and the edge of the band gap. (C) 2010 Elsevier Masson SAS. All rights reserved.

50. Optical spectroscopy of heavily Ho3+-doped BaY2F8 crystals

Authors: Tsuboi, T; Jang, KH; Polosan, S; Shimamura, K; Bettinelli, M; Seo, HJ

Published: APR 2011, JOURNAL OF LUMINESCENCE, 131, 700, DOI: 10.1016/j.jlumin.2010.11.020

The ultraviolet, visible, and near IR (0.8-2.4 mu m) luminescence spectra of BaY2F8 single crystals heavily doped with Ho3+ ions (10 and 30 mol%) have been investigated at room temperature and 12 K, together with the luminescence decay curves (up to 300 mu s) of the visible emission. Excitation in the visible region gives rise to very strong emission bands originating from the first I-5(7) level and located around 2070 nm. However the I-5(7) emission is not observed upon excitation at wavelengths shorter than 300 nm. The inter-ionic processes are found to shorten the decay times of the levels emitting in the visible region with respect to the corresponding radiative lifetimes. (C) 2010 Elsevier B.V. All rights reserved.

51. Green light radiation effects on free radicals inhibition in cellular and chemical systems

Authors: Comorosan, S; Polosan, S; Jipa, S; Popescu, I; Marton, G; Ionescu, E; Cristache, L; Badila, D; Mitrica, R

Published: JAN 10 2011, JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY, 102, 44, DOI: 10.1016/j.jphotobiol.2010.09.003

Free radicals generation is inhibited through green light (GL) irradiation in cellular systems and in chemical reactions. Standard melanocyte cultures were UV-irradiated and the induced cellular reactive oxygen species (ROS) were quantified by the fluorescence technique. The same cell cultures, previously protected by a 24 h GL exposure, displayed a significantly lower ROS production. A simple chemical reaction is subsequently chosen, in which the production of free radicals is well defined. Paraffin wax and mineral oil were GL irradiated during thermal degradation and the oxidation products checked by chemiluminescence [CL] and Fourier transform infrared spectra [FT-IR]. The same clear inhibition of the radical oxidation of alkanes is recorded. A quantum chemistry modeling of these results is performed and a mechanism involving a new type of Rydberg macromolecular systems with implications for biology and medicine is suggested. (C) 2010 Elsevier B.V. All rights reserved.

52. Structural changes during the crystallization of the Bi4Ge3O12 glasses

Authors: Polosan, S; Nastase, F; Secu, M

Published: FEB 1 2011, JOURNAL OF NON-CRYSTALLINE SOLIDS, 357, 1113, DOI: 10.1016/j.jnoncrysol.2010.10.016

Bismuth-germanate glass ceramics with the composition 40% Bi2O3-60% GeO2 (in molar percents) were prepared through controlled crystallization of melt-quenched glass. The Raman and FTIR spectra recorded in the as-made glasses show broad bands at 240, 400, 780 cm(-1) and 400, 745 cm(-1) have been assigned Ge-O bonds which appear right after preparation. X-ray diffraction has shown that the as-made glasses are amorphous, but after annealing above the crystallization temperature at 558 degrees C, BGO nano-crystallites with a size of about 50 nm precipitate in the glass matrix. The Raman and FTIR spectra reveal sharp peaks associated to the "internal" and "external vibrations" of GeO4 tetrahedral groups inside the BGO nano-crystallites. In the glass ceramic sample the transparency region is shifted at longer wavelengths compared to as-made glass, due to the Rayleigh scattering on the BGO nano-crystallites. (C) 2010 Elsevier B.V. All rights reserved.

53. Growth and optical characterization of Pb-, TI-doped LiF crystals

Authors: Somma, F; Montereali, RM; Vincenti, MA; Polosan, S; Secu, M

Published: AUG 2010, OPTICAL MATERIALS, 32, 1312, DOI: 10.1016/j.optmat.2010.04.038

Large and transparent LiF:Pb and LiF:TI crystals were successfully grown by using Kyropoulos method. They were characterized using spectroscopic measurements combined with differential thermal analysis and thermogravimetry (TG) analysis, in order to investigate the effect of dopants upon the optical properties of these crystals. The optical absorption peaks at 278 nm (for Pb) and 273 nm (for TI) have been assigned to the A-type transition of these ions. Photoluminescence spectra have shown bands at 350 nm (for TI) and 375 nm (for Pb), which have been associated to the dopant ions in different configurations in the lattice. (C) 2010 Elsevier B.V. All rights reserved.

54. Eulityte glasses - synthesis and characterization

Authors: Berbecaru, C; Alexandru, HV; Polosan, S

Published: 2010, PHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 7, NO 9, 7, DOI: 10.1002/pssc.200983770

Oxides glasses are suitable for electronic and optoelectronic applications (band gap higher than 3 eV). Eulytite glasses were obtained from Bi4GeO14 sintered powder or mixture oxides powders Bi2O3-GeO2. The powders rapidly heated and melted at 1050 degrees C for 5 divided by 10 min was poured on the graphite plates under the glass transition temperature. Structural SEM, XRD and EDX investigations were performed at room temperatures. The frequency dependence of the permittivity and loss (45 Hz divided by 5 MHz) was investigated on a large temperature range between -140 and +375 degrees C. The permittivity and loss increase with the temperatures increase and decrease with the frequency increase. An activation energy of 0.88 kcal/mol, comparable to the thermal energy RT = 0.65 kcal/mol, was found for cluster formation on 150 divided by 200 degrees C temperature range. The jump of permittivity on the range 275 divided by 325 degrees C suggest an incipient glass transition at lower temperatures than 400 degrees C, as usually is accepted. The permittivity increase, correlated with the dipolar polarization was noticed at higher temperatures. The decrease of permittivity and loss in 10 divided by 100 kHz frequency range, at the mentioned temperatures, supports this assertion. The estimated relaxation times suggest the big clusters formation. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

55. X-ray excited luminescence and photoluminescence of Bi-4(GeO4)(3) glass-ceramics

Authors: Polosan, S; Secu, M

Published: MAR-JUL 2010, RADIATION MEASUREMENTS, 45, 411, DOI: 10.1016/j.radmeas.2010.01.040

Bi-4(GeO4)(3) glass materials have been characterized by X-ray excited luminescence, photoluminescence and cathodo-luminescence measurements. The materials were obtained by crystallization at different temperatures and their spectroscopic parameters were compared before and after crystallization. Thermoluminescence curves recorded after electron irradiation of BGO glass behave similarly to BGO crystals, showing several peaks between 408 K (135 degrees C) and 610 K (337 degrees C). The differences between the Bi-4(GeO4)(3) crystals and glass materials are believed to result from the random distribution of GeO4 tetrahedra around Bi3+ ions which influences the photoluminescence and TL parameters. The CL images of glass-ceramic samples obtained by partial crystallization at 600 degrees C show luminescent crystalline structures, which are probably responsible for the increase in scintillation efficiency. (C) 2010 Elsevier Ltd. All rights reserved.

56. Structural studies on serum albumins under green light irradiation

Authors: Comorosan, S; Polosan, S; Popescu, I; Ionescu, E; Mitrica, R; Cristache, L; State, AE

Published: OCT 2010, EUROPEAN BIOPHYSICS JOURNAL WITH BIOPHYSICS LETTERS, 39, 1491, DOI: 10.1007/s00249-010-0606-y

This paper presents two new experimental results: the protective effect of green light (GL) on ultraviolet (UV) denaturation of proteins, and the effect of GL on protein macromolecular structures. The protective effect of GL was revealed on two serum albumins, bovine (BSA) and human (HSA), and recorded by electrophoresis, absorption, and circular dichroism spectra. The effect of GL irradiation on protein structure was recorded by using fluorescence spectroscopy and electrophoresis. These new effects were modeled by quantum-chemistry computation using Gaussian 03W, leading to good fit between theoretical and experimental absorption and circular dichroism spectra. A mechanism for these phenomena is suggested, based on a double-photon absorption process. This nonlinear effect may lead to generation of long-lived Rydberg macromolecular systems, capable of long-range interactions. These newly suggested systems, with macroscopic quantum coherence behaviors, may block the UV denaturation processes.

57. Dynamics of energy absorption versus crystallization in Bi4Ge3O12 (BGO) amorphous materials

Authors: Polosan, S

Published: OCT 2010, MATERIALS RESEARCH BULLETIN, 45, 1495, DOI: 10.1016/j.materresbull.2010.06.017

Theoretical and experimental determinations show that the intrinsic luminescence of BGO materials is strongly influenced by GeO4- tetrahedra around Bi3+ ions. Besides Bi3+ transitions, the excitonic spectra mask the BGO bandgap. Theoretical computations give the bandgap at 5.19 eV compared with the experimental one at 5.17 eV in BGO crystals and a significant decrease at 3.26 eV in the amorphous materials. This is due to the high disordering of the GeO4- tetrahedral which also reduces the refractive index of the amorphous materials. Formation of excitonic states and their overlap with the Bi3+ transitions suggests that the energy absorption takes place via the p-electrons of the O-2(-) ions and is then transferred to the Bi3+ p-electrons (excited states) close to the conduction band. Light emission appears after de-excitation to the ground state. (C) 2010 Elsevier Ltd. All rights reserved.

58. Optical and X-ray absorption spectroscopy in lead doped lithium fluoride crystals

Authors: Somma, F; Aloe, P; d'Acapito, F; Montereali, RM; Polosan, S; Secu, M; Vincenti, MA

Published: 2010, 11TH EUROPHYSICAL CONFERENCE ON DEFECTS IN INSULATING MATERIALS (EURODIM 2010), 15, DOI: 10.1088/1757-899X/15/1/012035

LiF:Pb doped crystals were successfully grown by Kyropoulos method, starting with drying powders. The presence of Pb2+ ions in the LiF crystals were evidenced by the absorption band at 278 nm and by 375 nm photoluminescence. The presence of some other Pb structures with oxygen compounds in the as made samples was evidenced, decreasing after some annealing procedures. The local environment and valence state of Pb in LiF were studied by X-ray Absorption Spectroscopy at the Pb L-III and L-I edges. XANES data reveal that Pb is present as Pb2+ whereas EXAFS data show that it is incorporated in the crystal and not forming PbF2 precipitates. Identical spectra are obtained for samples as prepared and after thermal annealing up to 650 degrees C demonstrating the stability of the incorporation site. Also the concentration of Pb in the crystal has no effect on the location site of the metal as the same spectrum is obtained for specimens with different dopant concentrations.

59. Synthesis of Eu-doped bismuth germanate nano-ceramic powder

Authors: Polosan, S; Matei, E; Logofatu, C

Published: OCT 2010, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 4, 1508, DOI:

Europium doped Bi(4)Ge(3)O(12) nanocrystals were successfully obtained by solid state reaction between precursor oxides at 800 degrees C. The XRD and XPS measurements shows an increasing of the lattice constant in the case of Eu:BGO nanocrystals, due to the electropositive character of Eu(III) ions compared with the host cations, which induces an ionic character for Eu-O bound and a more covalent one for the Ge-O bounds. The photoluminescence of Eu:BGO due to (5)D(0) -> (7)F(2) transition have a lower splitting compared with Eu:BGO monocrystals suggesting a lower crystal field in the sintered nanocrystals, due to a mixing between the crystalline and amorphous phases.

60. Radiation induced defects in Tl+-doped LiF crystals

Authors: Polosan, S; Secu, M; Logofatu, C; Somma, F; Montereali, RM; Vincenti, MA

Published: 2010, 11TH EUROPHYSICAL CONFERENCE ON DEFECTS IN INSULATING MATERIALS (EURODIM 2010), 15, DOI: 10.1088/1757-899X/15/1/012081

Tl+-doped lithium fluoride crystals exhibit very interesting properties concerning the formation of colour centres after X-rays irradiation. The presence of Tl+ ions, even in small concentrations, increases the number of traps which stabilize the H-centre aggregates. These H-centre aggregates become smaller and their number increases, inducing two sets of trapping levels. Photoluminescence measurements after subsequent thermal bleaching of the thermoluminescence peaks show a faster decreasing of the F-3(+) centres, in three steps, compared with the F-2 ones. The F-H recombination processes may induce the excitation-emission transitions of Tl+-ions.

61. Characterization of BGO glass-ceramic materials

Authors: Polosan, S

Published: OCT 1 2009, JOURNAL OF NON-CRYSTALLINE SOLIDS, 355, 1903, DOI: 10.1016/j.jnoncrysol.2009.04.061

Glass-ceramics of the compositions Bi(4)Ge(3)O(12) (BGO) and Bi(2)O(3)-GeO(2) have been obtained by pouring molten materials onto graphite plates heated below and above the glass transition temperatures. Glass transitions temperatures have been measured by DSC. T(g) is lower in the case of BGO than with the Bi(2)O(3)-GeO(2) glass ceramics material. Crystallization is evaluated by X-ray diffraction and microscopic observations. The XRD measurements confirm the amorphous structure of the samples cast below T(g). The Hruby factor, which measures the stability of the glass-ceramics, is about 0.21 in the case of BGO glass ceramics suggesting a rather stable glass. The fluorescence under U.V. excitation is larger by one order of magnitude in the case of BGO glass-ceramics by comparison to the Bi(2)O(3)-GeO(2) glasses, suggesting it is a good candidate for scintillation materials. The images obtained under U.V. excitation shows structured luminescent centers in the case of BGO glass-ceramics. (C) 2009 Elsevier B.V. All rights reserved.

62. Crystallization and spectroscopic properties of Eu-doped CaF2 nanocrystals in transparent oxyfluoride glass-ceramics

Authors: Secu, M; Secu, CE; Polosan, S; Aldica, G; Ghica, C

Published: OCT 1 2009, JOURNAL OF NON-CRYSTALLINE SOLIDS, 355, 1872, DOI: 10.1016/j.jnoncrysol.2009.04.062

Transparent oxyfluoride glass-ceramic in the system SiO2-Al2O3-CaF2-EuF2 containing Eu-doped CaF2 nanocrystals were produced by using the controlled crystallization of melt-quenched glass. X-ray diffraction and transmission electron microscopy data have revealed the formation of the CaF2 nanocrystals of about 65 nm size. Photoluminescence spectra have shown an increase of the splitting of the luminescences associated to the Eu3+ ion along with annealing time which is consistent with the Eu3+ environment evolving from a glassy to a crystalline state. (C) 2009 Elsevier B.V. All rights reserved.

63. Radiation induced defects in Pb2+-doped LiF crystals

Authors: Somma, F; Montereali, RM; Vincenti, MA; Polosan, S; Secu, M

Published: 2009, 2008 INTERNATIONAL CONFERENCE ON LUMINESCENCE AND OPTICAL SPECTROSCOPY OF CONDENSED MATTER, 2, 221, DOI: 10.1016/j.phpro.2009.07.013

The influence of Pb2+ doping on the optical properties of LiF crystals before and after irradiation with X-ray was studied by using optical absorption and photoluminescence measurements. After irradiation it was observed an increase of the absorption due to primary and aggregate electronic defects together with a higher photoluminescence signals associated with the F-2 and F-3(+) colour centres in doped samples compared with the undoped ones.

64. Density functional theory analysis of a mixed-ligand iridium compound for multi-color organic light-emitting diodes

Authors: Polosan, S; Chow, TJ; Tsuboi, T

Published: APR 2008, JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, 21, 320, DOI: 10.1002/poc.1329

Electronic states and their energies are calculated for a mixed-ligand Ir(III) compound, (5-chloro-8-hydroxyquinoline) bis(2-phenylpyridyl) iridium (called IrQ(ppy)(2)-5CI) using time-dependent density functional theory (TDDFT) calculations and are compared with the experimental result. A good agreement is obtained between the calculated and measured absorption spectra: The d-pi(Q)* molecular orbital transition gives the lowest-energy triplet state absorption band. Its energy is estimated as 1.84 eV (671 nm), which is close to the absorption band position of 1.86 eV (666 nm) observed for IrQ(ppy)(2)-5CI doped in 4,4'-NN'-dicarbazole-biphenyl (CBP) host and of 1.88 eV (660 nm) observed for IrQ(ppy)(2)-5CI doped in polystyrene (PS). The second triplet state absorption band is caused by d-pi(ppy) transition. Its position is calculated as 2.51 eV (494 nm). The dipole moment is estimated as 3.45 D, which is lower than the dipole moment of fac-Ir(ppy)(3). This is understood by a reduced charge transfer between Ir(III) and quinoline ligand. Copyright (C) 2008 John Wiley & Sons, Ltd.

65. Optical spectroscopy and thermoluminescence of electrolytically colored KCl:Tl+ crystals

Authors: Polosan, S; Enculescu, M; Secu, M; Apostol, E

Published: NOV 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 3011, DOI:

The paper presents the spectroscopic properties of electrolytic colored KCl:Tl and KCI:Tl+Ca crystals and the assignments of the new defects which are formed during electron injection process. The new formed defects Tl-0 and Tl-0+Ca2+ with the metal in the anionic sites, presents very high photoluminescence properties in the near infrared region. Together with those centers, the F-centers, their aggregates and the holes centers are formed during electrolytic coloring process. Their properties were studied by optical absorption (OA), photoluminescence (PL) and thermoluminescence (TL) measurements and compared with those obtained by ionizing irradiation in uncolored KCl:Tl crystals. The results suggest a more efficient Tl+-> Tl-0 process in the case of Ca2+ codoped samples due to the prolonged time of electrons injection, low temperature and high electric field.

66. Optical properties of CaF2 : Eu3+ nanoctystals embedded in transparent oxyfluoride glass ceramic

Authors: Polosan, S; Secu, CE

Published: AUG 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 2137, DOI:

Transparent oxyfluoride glass ceramic in the system SiO2-Al2O3-CaF2-EuF2 containing CaF2:Eu3+ nanocrystals were produced by annealing of the initial glasses slightly above the CaF2 phase crystallisation peak. The relative good transparency of these materials was due to the small 65 nm, nucleated CaF2 nanocrystallites. X-ray diffraction data have shown an increase of the cell parameters for CaF2:Eu3+ compared with CaF2 which was attributed to the substitution of Ca2+ ions with Eu3+ ions in the CaF2 nanoparticles. Optical investigations using UV-VIS-NIR absorption and luminescence spectroscopy have shown an increase of the splitting of the Eu3+-ion associated luminescences and small shifts of the Eu3+ ion characteristic IR absorption peaks. These effects have been attributed to the Eu3+ environment evolving from the glass to the crystalline-like one.

67. Photoluminescence processes in Er3+-doped calcium niobium gallium garnet (CNGG) crystals

Authors: Polosan, S; Shimamura, K; Tsuboi, T

Published: MAR 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 532, DOI:

Photoluminescence properties of Er3+-doped calcium niobium gallium garnet (CNGG) disordered crystals have been studied in the range of 200-2000 nm at 10-290 K. In addition to emission bands due to Er3+, a broad emission band is observed at 470 nm. From the emission spectra that were obtained by various excitations, level assignment has been established for the emission bands. Different temperature dependences are observed between the emission bands at 522 and 543 nm. This is explained using non-radiative phonon relaxation between the H-2(11/2) and S-4(3/2) states. Besides the 1535 nm Er3+ emission band, near infrared emission bands are observed at 860 and 1240 nm, which are attributed to the transitions from the S-4(3/2) state to the (4)vertical bar(13/2) and vertical bar 4(11/2) states, respectively.

68. New perturbed Pb--aggregate centers in electrolytically colored KBr : Pb2+ + (Ca, Ba) crystals

Authors: Polosan, S; Topa, V; Apostol, E; Tsuboi, T

Published: JAN-APR 2007, JOURNAL OF LUMINESCENCE, 122, 948, DOI: 10.1016/j.jlumin.2006.01.364

New luminescent centers with a large near-infrared emissions were obtained by unusual electrolytic coloration method (low temperature and high electric field) in the KBr:Pb2+ crystals co-doped with alkali-earth ions (Ca2+, Sr2+, Ba2+). These so-called Tx centers involve Pb--negative metal ions and the presence of at least one alkali-earth ion, which enhances the photoluminescence properties of those centers. The formation of these new centers is due to the presence of F-centers created in the process of electrolytical coloration. The photoluminescence properties, together with the magnetic circular dichroism spectra, prove the existence of at least one paramagnetic luminescent center. (c) 2006 Elsevier B.V. All rights reserved.

69. Electrolytic reduction of Tl+ ions in KCl crystals

Authors: Polosan, S; Tsubi, T; Apostol, E; Topa, V

Published: SEP 2007, OPTICAL MATERIALS, 30, 97, DOI: 10.1016/j.optmat.2006.11.006

Electrolytic coloration has been made for KCl crystals doped with Tl+ ions and doped with Tl+ and Ca2+ ions. Intensity decrease of the Tl+ absorption bands is observed in the two colored crystals, while several new absorption and emission bands are observed. They are attributed to Tl- ions which were converted from Tl+ ions by electron injection during electrolytic coloration. Different absorption and emission bands are observed for KCI:TI and KCI:T1 + Ca crystals. Sharp absorption band appears at 285 nm in the colored KCl:Tl and at 400 and 503 nm in the colored KCLTl + Ca. Infrared emission bands are observed at 1470, 1600 and 2185 nm in colored KCI:Tl, while at 1630 and 1900 nm in colored KCl:Tl + Ca. It is suggested that the absorption and emission bands in KCl:Tl + Ca are due to Tl- ions perturbed by Ca2+ or vacancy at the nearest neighbor. (c) 2006 Elsevier B.V. All rights reserved.

70. Lithium deposition on high energy irradiated LiF crystals

Authors: Polosan, S

Published: MAY 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 1309, DOI:

Lithium metallic colloids were studied in ion-implanted LiF crystals, irradiated with high energy He+ particles. The presence of metallic particles, displaying absorption bands at 420 and 460 nm due to the scattering of light on these particles, overlaps the absorption of M centers. The luminescence excited in this band, which is a superposition between the absorption of F-2 and F-3(+) centers, is reduced due to the metallic lithium particles, formed on the surface of the irradiated and at the end of the tracks of He+ particles, reducing the luminescence of the formed color centers. Diminution of the M band together with the growing of the 420 nm band versus irradiation doses, suggest a transformation of the color centers in small Fn-aggregates during the irradiation process, followed by a metallic conversion of Li ions.

71. Tin nanoclusters obtained in potassium chloride by thermal annealing

Authors: Apostol, E; Enculescu, M; Polosan, S; Vasile, E; Topa, V

Published: 2007, PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 4, NO 3, 4, +, DOI: 10.1002/pssc.200673734

Tin nanoclusters were obtained in potassium chloride crystals following the electrolytic coloration of KCl:Sn2+ and KCl:Sn2++Ca2+ crystals and thermal annealing at various temperatures and times. Electrolytic coloration of KCl:Sn2+ crystals produces electronic centers inside of samples, presumably negative metal ions of tin. Optical absorption measurements were performed on as grown sample, colored and thermal annealed samples. The behavior of the samples with Sn colloids was compared with theoretical predictions according to Mie's theory. Tin nanoclusters in KCl exhibit an absorption band with a peak at 215 nm. The structure of the nanoclusters was studied by optical absorption and transmission electron microscopy means. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

72. Emission properties of T-a-centres in KCl

Authors: Topa, V; Tsuboi, T; Polosan, S

Published: AUG-DEC 2004, RADIATION MEASUREMENTS, 38, 734, DOI: 10.1016/j.radmeas.2004.01.021

Electrolytic colouration at about 600degreesC and 350 V/cm, for KCl crystal containing Pb2+ and for KCl:Pb2+ crystals co-doped with Li+, Na+ and Rb+ has been undertaken. Several absorption bands were observed in both doped and co-doped crystals in the visible-UV region. Excitation into these bands gives rise to the same 0.86 eV emission band except for the Li+-co-doped crystal which gives rise to a 0.80 eV emission band. These absorption bands are due to the same T-a-centre related to Pb-. The observed infrared emission intensity of the crystal with F-centres is higher than of without F-centres. (C) 2004 Elsevier Ltd. All rights reserved.

73. Isolated nanocrystals of indium in KCl crystals

Authors: Polosan, S; Apostol, E; Vasile, E; Topa, V

Published: SEP 2003, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 5, 704, DOI:

Metal nanoparticles embedded in KCl crystals exhibit different forms and distributions, depending on the type of metal. The nanoparticles can be efficiently studied by optical absorption on these structures, calculated from Mie theory and comparison with Transmission Electron Mmicroscopy (TEM) measurements. The TEM images provide the detailed characteristics of the structures under study. Metal crystalline particle obtained by thermal treatments of negative indiurn ions are spherical. The particle size distribution was determined, the standard deviation was found 1.46, and the main statistical characteristics were calculated.

74. Negatively charged Pb- ion produced by electrolytical colouration of KCl crystals containing Li+, Na+ and Rb+ ions

Authors: Tsuboi, T; Polosan, S; Topa, V

Published: AUG 5 2002, JOURNAL OF PHYSICS-CONDENSED MATTER, 14, 7272, DOI: 10.1088/0953-8984/14/30/315

Electrolytic colouration has been undertaken for not only a KCl crystal containing Pb2+ ions but also KCl crystals containing alkali impurity ions (Li+, Na+ and Rb+) besides Pb2+ ions. Absorption spectra of these electrolytically coloured crystals have been studied, together with the emission spectra. Similar spectra were observed among these crystals. Eight weak absorption bands are observed in the 290-700 nm region, while five intense bands are observed in the 200-290 nm region. It is suggested-that these bands arise from Pb- ions with tetragonal crystal field symmetry. The energy-level assignment for these absorption bands is made using the energy-level diagram of the isoelectronic Bi-0 atom with C-4v crystal field symmetry. It is suggested that an off-centre position effect of the Li+ ion is observed in the kCl crystal codoped with Li+ ions.. Broad emission bands at 1530 and 1580 nm have been. observed in electrolytically coloured KCl containing Pb2+ ions and KCl containing Li+ and Pb2+ ions, irrespectively.

75. Chemical composition of structures obtained inside quartz crystals by sodium electrodiffusion

Authors: Iliescu, B; Enculescu, I; Pera, I; Alexe, G; Polosan, S; Stanculescu, A

Published: 2001, CRYSTAL RESEARCH AND TECHNOLOGY, 36, 410, DOI: 10.1002/1521-4079(200106)36:4/5<403::AID-CRAT403>3.0.CO;2-H

Dendritic structures were grown inside quartz crystals by electrodiffusion of sodium ions from a NaCl layer at the anode. An experimental arrangement using a point cathode and a graphite plate anode was employed. X-ray diffraction experiments were carried out, the structures chemical composition was found to be a mixture of sodium silicates. The chemical composition evolution in time was observed. There were made VIS and UV optical absorption spectroscopy measurements of these structures, a colloidal band being found. Thermoluminescence glow curves were measured. Based on the experimental results and observations a growth model is proposed.

76. Lead nanocrystals in KCl matrix

Authors: Polosan, S; Vasile, E; Apostol, E; Topa, V

Published: MAR 2001, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 3, 140, DOI:

77. The Pb(2+)(Li) and Pb(2+)(Na) centres in KCl crystals

Authors: Tsuboi, T; Polosan, S; Topa, V

Published: FEB 2000, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 217, 980, DOI: 10.1002/(SICI)1521-3951(200002)217:2<975::AID-PSSB975>3.0.CO;2-U

Emission, absorption and magnetic circular dichroism spectra have been studied on Li(+)- and Pb(2+)-codoped KCl crystals. Two emission bands (one is the A(T)-like emission and the other the A(X)-like emission) have been observed at 350 and 453 nm at room temperature, respectively These emissions have been observed by excitation in the absorption bands with peaks at 270 and 281 nm. These emission bands are attributed to the Pb(2+)(Li) centre, where a Pb(2+) ion has a Li(+) ion at one of the six nearest neighbouring cation sites. Measurements have been also made on Na(+)- and Pb(2+)-codopcd KCl crystals. Unlike the Pb(2+)(Li) centre, only the A(T)-like emission band with a peak at 347 nm due to the Pb(2+)(Na) centre has been observed. It is suggested that such a difference is due to a difference in the position of the impurity alkali ion substituted for the K(+) ion.

78. Properties of metal clusters embedded in KCl matrix

Authors: Polosan, S; Apostol, E; Topa, V

Published: 2000, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 2, 642, DOI:

The characterization of nanocrystals embedded in alkali halide crystals concerning shape and size distribution has been performed. Optical absorption, transmission electron microscopy (TEM), x-ray diffraction (XRD) and electron spin resonance (RES) methods has been used. The experimental results are in good agreement with the theoretical considerations concerning absorption and scattering of light by the metal clusters.

79. Silver nanocrystals obtained by the ionization of Ag--ions in KCl

Authors: Vasile, E; Datcu, M; Polosan, S; Apostol, E; Topa, V

Published: MAR 1999, JOURNAL OF CRYSTAL GROWTH, 198, 810, DOI: 10.1016/S0022-0248(98)01112-9

This paper discusses the formation of "corals" arranged silver nanocrystals in a KCl matrix starting from Ag- ions ( similar to 10(17) ions/cm(3)) by subsequent thermal annealing at temperatures between 400-700 degrees C and 250 degrees C. In the last case only, by illumination with total radiation of a 100W Xe-lamp, spherical separated silver clusters were obtained. The stepwise annealing processes were followed by the recording of the optical absorption spectra at 20 degrees C. The sizes of silver clusters were determined through transmission electron microscopy. (C) 1999 Published by Elsevier Science B.V. All rights reserved.

80. On the determination of birefringence of liquid crystals by the interference method

Authors: Moldovan, R; Tintaru, M; Frunza, S; Beica, T; Polosan, S

Published: 1996, CRYSTAL RESEARCH AND TECHNOLOGY, 31, 955, DOI: 10.1002/crat.2170310724

A new method of processing the experimental data in the interference method for the determination of birefringence of liquid crystals which allows obtaining results in good agreement with those from prism or wedge methods, is presented.

81. Highly Conductive Carbon-Based Thin Films Produced by Low-Energy Electron Irradiation

Authors: Ciobotaru, CC; Ciobotaru, IC; Iosub, DG; Polosan, S

Published: , JOURNAL OF ELECTRONIC MATERIALS, DOI: 10.1007/s11664-021-09058-5

Dr. Silviu POLOSAN

Scientific Researcher I

Projects

1. Highly conductive and transparent metallic electrodes for Organic Light-Emitting Diodes

2. Dual emitters for displays based on oled compounds.

Publications

1. Charge transport mechanisms in free-standing devices with electrospun electrodes

2. The Synergistic Effect of the Laser Beam on the Thermionic Vacuum Arc Method for Titanium-Doped Chromium Thin Film Deposition

3. Magnetic Core-Shell Iron Oxides-Based Nanophotocatalysts and Nanoadsorbents for Multifunctional Thin Films

4. Electronic and transport properties of the dual-emitter organometallic compound IrQ(ppy)(2)

5. Highly Conductive Carbon-Based Thin Films Produced by Low-Energy Electron Irradiation

6. Structural features, magnetic and ferroelectric properties of SrFe10.8In1.2O19 compound

7. The origin of the dual ferroic properties in quasi-centrosymmetrical SrFe12-xInxO19 hexaferrites

8. Magnesium-silver cathodes for efficient charge injection into Organic Light Emitting Diodes deposited by LTVA method

9. Structural, magneto-optical and dielectric properties of phosphate tellurite glasses

10. Synthesis and characterization of magnetic oxide nanoparticles and corresponding thin films for wastewaters treatment

11. Detailed Molecular and Structural Analysis of Dual Emitter IrQ(ppy)(2) Complex

12. ZnO nanostructures grown on ITO coated glass substrate by hybrid microwave-assisted hydrothermal method

13. Magnetic and ferroelectric properties, crystal and magnetic structures of SrFe11.9In0.1O19

14. Crystal and magnetic structures, magnetic and ferroelectric properties of strontium ferrite partially substituted with in ions

15. Optical spectroscopy and dielectric properties of phosphate-tellurite glasses

16. Organometallic Coatings for Electroluminescence Applications

17. Sol-Gel Processing of Bismuth Germanate Thin-Films

18. Charge Transfer from Alq(3)-5Cl to Graphene Oxide in Donor-Acceptor Heterostructures

19. Efficiency enhancement of iridium-based organometallic light emitting diodes

20. Structure and low field magnetic properties in phosphate-tellurite glasses

21. Crystallization processes in europium-doped Bi4Ge3O12 glass materials

22. Organometallic compounds for photovoltaic applications

23. Charge carrier traps in tris-(8-hydroxyquinoline) aluminum

24. Electroluminescence Properties of IrQ(ppy)(2) Dual-Emitter Organometallic Compound in Organic Light-Emitting Devices

25. Low energy electron irradiation of carbon thin films

26. Crystallisation of bismuth germanate glasses below their glass transition temperature

27. Crystallization properties of IrQ(ppy)(2) organometallic complex films

28. Enhancement of the electroluminescence of organic light emitting devices based on Ir(ppy)(3) by doping with metallic and magnetic nanoparticles

29. Templateless electrodeposition ZnO nanowires for charge transport optimization in OLED structures

30. STRUCTURAL AND MORPHOLOGICAL EVOLUTIONS INDUCED BY THE ANNEALING OF CaF2 NANOCRYSTALLINE POWDERS BY USING Eu3+ ION PROBE LUMINESCENCE

31. Ferromagnetic behaviour of bismuth germanate oxides glass-ceramic materials

32. Absorption, phosphorescence and Raman spectra of IrQ(ppy)(2) organometallic compound

33. Conformational changes and metastable states induced in proteins by green light

34. Thermally activated conversion of a silicate gel to an oxyfluoride glass ceramic: Optical study using Eu3+ probe ion

35. Structural characteristics of iridium dual-emitter organometallic compound

36. COVALENT FUNCTIONALIZATION OF SINGLE WALLED CARBON NANOTUBES WITH DOXORUBICIN FOR CONTROLLED DRUG DELIVERY SYSTEMS

37. DRUG DELIVERY STUDY OF SINGLE-WALL CARBON NANOTUBES COVALENT FUNCTIONALIZED WITH CISPLATIN

38. Embedding of IrQ(ppy)(2) organometallic compounds in polypyrrole conducting polymer for OLED's applications

39. Dual emitter IrQ(ppy)(2) for OLED applications: Synthesis and spectroscopic analysis

40. Mechanisms of the Charge Transfer in IrQ(ppy)(2)-5Cl Dual-Emitter Compound

41. Optical manipulation of complex molecular systems by high density green photons: experimental and theoretical evidence

42. Lead incorporation mechanism in LiF crystals

43. Antioxidant effects induced in biological macromolecular systems by high density photons through localized excitations

44. Cathodoluminescence and Raman analysis of the finite-size effects in mer-Alq(3) structure

45. HIGH-DENSITY GREEN PHOTONS EFFECTS ON NaCl SOLUTIONS DETECTED BY RED BLOOD CELLS MEMBRANES

46. Photoluminescence and magnetic circular dichroism of IrQ(ppy)(2)-5Cl

47. Investigations of the non-isothermal crystallization of Bi4Ge3O12 (2:3) glasses

48. Magneto-optical investigations of rare earth doped sol-gel derived silicate xerogels

49. Band-gap correlations in Bi4Ge3O12 amorphous and glass-ceramic materials

50. Optical spectroscopy of heavily Ho3+-doped BaY2F8 crystals

51. Green light radiation effects on free radicals inhibition in cellular and chemical systems

52. Structural changes during the crystallization of the Bi4Ge3O12 glasses

53. Growth and optical characterization of Pb-, TI-doped LiF crystals

54. Eulityte glasses - synthesis and characterization

55. X-ray excited luminescence and photoluminescence of Bi-4(GeO4)(3) glass-ceramics

56. Structural studies on serum albumins under green light irradiation

57. Dynamics of energy absorption versus crystallization in Bi4Ge3O12 (BGO) amorphous materials

58. Optical and X-ray absorption spectroscopy in lead doped lithium fluoride crystals

59. Synthesis of Eu-doped bismuth germanate nano-ceramic powder

60. Radiation induced defects in Tl+-doped LiF crystals

61. Characterization of BGO glass-ceramic materials

62. Crystallization and spectroscopic properties of Eu-doped CaF2 nanocrystals in transparent oxyfluoride glass-ceramics

63. Radiation induced defects in Pb2+-doped LiF crystals

64. Density functional theory analysis of a mixed-ligand iridium compound for multi-color organic light-emitting diodes

65. Optical spectroscopy and thermoluminescence of electrolytically colored KCl:Tl+ crystals

66. Optical properties of CaF2 : Eu3+ nanoctystals embedded in transparent oxyfluoride glass ceramic

67. Photoluminescence processes in Er3+-doped calcium niobium gallium garnet (CNGG) crystals

68. New perturbed Pb--aggregate centers in electrolytically colored KBr : Pb2+ + (Ca, Ba) crystals

69. Electrolytic reduction of Tl+ ions in KCl crystals

70. Lithium deposition on high energy irradiated LiF crystals

71. Tin nanoclusters obtained in potassium chloride by thermal annealing

72. Emission properties of T-a-centres in KCl

73. Isolated nanocrystals of indium in KCl crystals

74. Negatively charged Pb- ion produced by electrolytical colouration of KCl crystals containing Li+, Na+ and Rb+ ions