National Institute Of Materials Physics - Romania

Publications

860 articles found

661. Influence of dye concentration on optical properties of rhodamine 6G doped KAP crystals

Authors: Enculescu, M; Matei, E; Preda, N; Enculescu, I

Published: NOV 2009, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 3, 1212, DOI:

Crystals of potassium acid phthalate (KAP) doped with rhodamine 6G (Rh 6G) were grown by slow evaporation method from aqueous solutions. Crystals of good optical quality suitable for optical applications were obtained. Different concentrations of rhodamine 6G (10(-5) M, 2x10(-5) M, 5x10(-5) M and 10(-4) M in the growth solutions) were used in order to tune the optical properties of the crystals. Depending of the dye concentration, the absorption spectra of the dye-doped crystals show several bands in the range between 360 nm and 526 nm. The photoluminescence of the KAP crystals induced by the dye-doping reveals two emission bands peaking at 540 nm and 560 nm.

662. 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.

663. 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.

664. Optical properties of CdS electrodeposited nanowires

Authors: Matei, E; Preda, N; Enculescu, M; Sima, M; Sima, M; Enculescu, I

Published: OCT 2009, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 3, 1022, DOI:

Electrochemical deposition was performed in order to prepare CdS nanowires. The method employed for preparation of such high aspect ratio nanostructures was template replication. Ion track polycarbonate membranes were used as templates. The nanowires were studied by scanning electron microscopy (morphology characterization), energy dispersive X ray analysis (composition) and optical spectroscopy. Optical reflection spectroscopy was performed in order to determine the band gap value while photoluminescence spectroscopy was used for getting information regarding the point defects in the material.

665. Sol-gel doped TiO2 nanomaterials: a comparative study

Authors: Raileanu, M; Crisan, M; Dragan, N; Crisan, D; Galtayries, A; Braileanu, A; Ianculescu, A; Teodorescu, VS; Nitoi, I; Anastasescu, M

Published: SEP 2009, JOURNAL OF SOL-GEL SCIENCE AND TECHNOLOGY, 51, 329, DOI: 10.1007/s10971-009-2017-z

Among the great number of sol-gel prepared nanomaterials, TiO2 has attracted significant interest due to its high photocatalytic activity, excellent functionality, thermal stability and non-toxicity. The photocatalytic degradation of pollutants using un-doped and doped TiO2 nanopowders or thin films is very attractive for applications in environmental protection, as a possible solution for water purification. The present work describes a comparative structural and chemical study of un-doped TiO2 and the corresponding S- and Ag-doped materials. The photocatalytic activity was established by testing the degradation of organic chloride compounds from aqueous solutions. Sol-gel Ag-doped TiO2 coatings, prepared by co-gelation and sol-gel Ag-doped TiO2 coatings obtained from nanopowders were also compared. Their structural evolution and crystallization behaviour (lattice parameters, crystallite sizes, internal strains) with thermal treatment were followed by thermal analysis, X-ray diffraction, transmission electron microscopy, atomic force microscopy and specific surface areas measurements. X-ray photoelectron spectroscopy analyses were performed to characterize the surface composition and S or Ag speciation, which was used to interpret the catalytic data.

666. Structural investigations of sol-gel derived silicate gels using Eu3+ ion-probe luminescence

Authors: Secu, CE; Predoi, D; Secu, M; Cernea, M; Aldica, G

Published: SEP 2009, OPTICAL MATERIALS, 31, 1748, DOI: 10.1016/j.optmat.2009.05.009

Undoped and Eu3+-doped CaF2-SiO2 gels were prepared by the sol-gel method and their optical properties have been studied. The UV-VIS-NIR absorption and photoluminescence spectra have shown the bands typical for the Eu3+ ions transitions. When the Eu-doped gel is annealed at temperatures up to 800 degrees C (i.e. above the CaF2 crystallisation peak at similar to 460 degrees C) the photoluminescence spectra intensity increase, the 590 nm (D-5(0) -> F-7(1)) and 620 nm (D-5(0) -> F-7(2)) luminescence bands become comparable and a structuring of the 620 nm band is observed. The phonon sidebands peaks associated with the F-5(0) -> D-7(2) transition of the Eu3+ ion were observed at around 1000 and 620 cm(-1) and have been assigned to the Si-O and Ca-O bonds, respectively. A phonon sideband signal in the range of 3007400 cm(-1) was attributed to Ca-F bonds in the precipitated CaF2 phase. From the optical absorption, photoluminescence and phonon sidebands spectra we have concluded that in the gels annealed at 800 degrees C, the Eu3+ ions are incorporated into the silica network and in the precipitated CaF2 phase. (c) 2009 Elsevier B.V. All rights reserved.

667. Chalcogenide photonic structures

Authors: Popescu, M; Savastru, D; Popescu, A; Miclos, S; Lorinczi, A; Sava, F; Velea, A; Baschir, L; Ciobanu, M; Matei, E; Socol, G; Mihailescu, IN; Niciu, H

Published: SEP 2009, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 3, 859, DOI:

Chalcogenide glasses can be tailored for getting special configurations with photonic crystal properties A review on the advances in chalcogenide glass photonics is given Several methods to prepare two-dimensional photonic As-S glass and three-dimensional packing have been developed, and the photonic structures have been characterized Numerical simulations have also been performed The chalcogenide photonic structures fabricated by micro-technological procedures are described and tuned to work in the far infrared region of the electromagnetic spectrum

668. Intercalation of Layered Metal Iodides with Pyridine Evidenced by Raman Spectroscopy

Authors: Preda, N; Mihut, L; Baibarac, M; Baltog, I

Published: JUL 2009, ACTA PHYSICA POLONICA A, 116, 83, DOI: 10.12693/APhysPolA.116.81

PbI2, BiI3, CdI2 and AgI crystalline samples intercalated with pyridine have been studied by Raman spectroscopy. Comparing the Raman spectra of pristine metal iodides with those of intercalated samples we have shown the coexistence, in the host crystalline lattice, of two adsorbed forms: a physisorbed one, featured by weak forces of van der Waals type and a chemisorbed one, involving stronger forces related to an electrostatic interaction. The physisorbed form is consistent with the molecules inserted into the interlayer spaces while the chemisorbed form is represented by the molecules forming coordination complexes with the crystalline lattice cations. The crucial role in the formation of such complexes is played by the lone pair of nitrogen atom belonging to the molecules.

669. Synthesis and ultrasonic characterization of hydroxyapatite ceramic powders

Authors: Predoi, D; Derible, S; Duflo, H

Published: JUN 2009, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 11, 856, DOI:

Calcium phosphate compounds have been studied for biomedical applications due to chemical and structural similarity to the mineral phase of bone and tooth. The composition, physico-chemical properties, crystal size and morphology of synthetic apatite are extremely sensitive to preparative conditions and sometimes it resulted into non-stoichiometric calcium deficient hydroxyapatite (HAp) powders. The present paper refers to calcinations of hydroxyapatite ceramics at 600, 800 and 1000 degrees C. The effect of heat treatment was previously investigated by X-ray diffraction (XRD). The ultrasonic characterisation of hydroxyapatite powders were performed using the ultrasonic air-coupling technique. Modulated ultrasonic signals of 450 kHz central frequency have been transmitted through the hydroxyapatite ceramics specimens. Correlation between signals allowed some conclusions concerning density, attenuation and preparation temperature influence on these specimens. These comparisons and correlation of methods, allow a better characterization of such important materials.

670. Titanium oxide thin films produced by pulsed laser deposition

Authors: Sima, C; Grigoriu, C; Viespe, C; Pasuk, I; Matei, E

Published: JUN 2009, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 11, 830, DOI:

The structural peculiarities of titanium oxide films formed by pulsed laser deposition have been investigated. A pure titanium target was irradiated by a Nd:YAG laser (355 and 532 nm). The work studied the influence of the beam wavelength, and oxygen pressure (20, 40, 80, and 160 mTorr) upon the layer structure. The films deposited at room temperature were partly crystalline. The crystalline fraction was a mixture of titanium sub-oxides. The 532 nm wavelength seems to favour the oxidation of titanium leading to TiO(2) formation even at room temperature. After annealing, crystalline TiO(2-) anatase formed at both irradiation wavelengths, but only at low oxygen pressures (20 and 40 mTorr). The best crystallization occurs in the layers deposited at the lowest oxygen pressure (20 mTorr), at both laser beam wavelengths; most anatase formed in the sample obtained at 20 mTorr, 532 nm. At 20 mTorr the films were compact, for both wavelengths, but also tilted or randomly distributed columnar grains were observed at higher pressure. The films deposited with 355 nm, were thinner than those with 532 nm; at 355 nm the thickness decreased at higher pressure, while at 532 nm the dependence was opposite.