National Institute Of Materials Physics - Romania

Lanthanide (Ln) co-doped transition metal (TM) upconversion (UC) co-doped systems are being intensively investigated for their exciting applications in photonics, bioimaging, and luminescence thermometry. The presence of TM, such as Mo6 + /W6 +, Mn2 +, or Fe3 + determines significant changes in Ln UC emission, such as intensity enhancement, colour modulation, and even the alteration of the photon order. The current mechanism assumes a ground-state absorption/excited-state absorption (ESA/GSA) in TM-Yb dimer followed by direct energy transfer to Er/Tm excited states. We revisit this mechanism by addressing two issues that remain ignored: a dynamical approach to the investigation of the upconversion mechanism and the intrinsic chemical complexity of co-doped TM, Ln systems. To this aim, we employ a pulsed, excitation variable laser across a complete set of UC measurements, such as the emission and excitation spectra and emission decays and analyze multiple grains with transmission electron microscopy (TEM). In the Mo co-doped garnet, the results sustain the co-existence of Mo-free garnet and Mo oxide impurity. In this Mo oxide, the Er upconversion emission properties are fully explained by a relatively efficient sequential Yb to Er upconversion process, with no contribution from Yb-Mo dimer sensitization.

In the present work, nanocrystalline NixCo1-xFe2O4 oxides with average crystallite size between 11 nm and 111 nm have been analyzed by Mossbauer spectroscopy, hysteresis loops, field cooled (FC) and zero field cooled (ZFC) magnetization measurements. A core-shell model has been proposed. Accordingly, the Mossbauer spectra evidence a ferrimagnetic core and a disordered shell (spin-glass), the latter increasing with Ni concentration. Hysteresis curves reveal the ferromagnetic nature of the investigated compounds and transformation from single- to multi-domain behaviour at a critical particle size dependent on Ni2+ ion concentration. The magnetic properties of finest powders (average crystallite size similar to 11 nm) are the most sensitive to the Ni2+ ions content. A general increase in the coercive field, H-C, with reducing temperature according to the modified Kneller's formula H-c(T) = H-c(0)[1-(T/T-B)(beta) where beta = 0.45 occurs. A high saturation magnetization of about 90 emu/g and an increase in H-C from about 0.3 kOe at 300 K to 7 kOe at 10 K have been observed for the sample Ni0.1Co0.9Fe2O4 (x = 0.1). Increasing magnetization and coercive field with reducing temperature are also explained within the core shell model. FC and ZFC data show strong dependence of the magnetic properties on crystallite size and concentration of Ni2+ ions.

Yttrium iron garnet nanoparticles were exposed to mechanochemical activation by high-energy ball milling for 0, 2, 4, 8 and 12 h, with and without graphene nanoparticles. The samples were subsequently characterized by Mo center dot ssbauer spectroscopy, X-ray powder diffraction (XRPD), magnetic measurements and optical diffuse reflec-tance spectroscopy. Examination of the quadrupole doublet's abundance as function of ball milling time indi-cated that graphene slowed down the precipitation of the yttrium iron perovskite (yttrium orthoferrite) phase. The increased linewidth of the doublet showed that the carbon from graphene preferentially entered the lattice of the yttrium orthoferrite. The saturation magnetization decreased with decreasing particle size for prolonged milling due to the occurrence of the antiferromagnetic hematite phase. The enhanced absorption in the infrared region could be associated with the incorporation of carbon from graphene in the lattice of the yttrium ortho-ferrite. The results are interesting for sensing and microwave applications.

A sensor for the enzymatic activity and inhibition of the 20S proteasome was developed by immobilizing the synthetic peptide ABZ-VVSYAMG-(O2Oc)2-OH at Au electrodes. The detection principle is based on the elec-troactivity of ABZ, part of the ABZ-VVSY-OH moiety released from the peptide upon 20S proteasome chymo-trypsin action. The peptide was immobilized on a para-amino thiophenol (PATP) self-assembled monolayer on Au electrode by cross-linking its amino group to the -(O2Oc)2-OH moiety of the peptide (Au/PATP/peptide). The immobilization of the peptide and its interaction with 20S proteasome was investigated by SEM, QCM, SPR, ATR-FTIR and electrochemistry. The activity of 20S proteasome was assessed electrochemically by cyclic voltammetry (CV) and electrochemical impedance spectra (EIS) after the immersion Au/PATP/peptide in 20S proteasome solution. CV study showed a decrease in both capacitive and faradaic currents corresponding to the ABZ-VVSY-OH removal, allowing the quantification of the 20S proteasome activity. The EIS study revealed that the resis-tance corresponding to charge transfer reactions at the peptide/solution interface correlated to the ABZ redox reaction, decreased linearly with increasing the incubation time in 20S proteasome solution. The perfected assay was applied for the investigation of the inhibitory effect of one synthetic, bortezomib, and two naturally occurring, epoxomicin, and lactacystin inhibitors.

The technology of perovskite solar cells (PSC) is getting close to breaching the consumer market. Yet, one of the current challenges is to reduce the toxicity during their fabrication by reducing the use of the toxic solvents involved in the perovskite fabrication process. A good solubilization of lead halides used in hybrid perovskite preparation is required, and it is only possible with polar solvents. A mixture of dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) is the most popular solvent combination for a perovskite precursor solution. DMF is necessary to ensure a good dissolution of lead iodide, but it is also the most toxic solvent. In this paper, we study the replacement of the dimethylformamide with presumably less toxic alternatives, such as N-methyl-2-Pyrrolidone (NMP) and ethyl acetate (EA), for the preparation of the K(0.1)FA(0.7)MA(0.2)PbI(2.8)Cl(0.2) (KFAMA) hybrid perovskite. The perovskite thin films were investigated by various characterization techniques: X-ray diffraction, atomic force microscopy, scanning electron microscopy, and UV-vis spectroscopy, while the photovoltaic parameters were determined by measuring the IV curves of the corresponding solar cells. The present study shows that by keeping the same deposition parameters as when only DMF solvent is used, the partial solvent substitution with NMP and EA gives promising results for reducing the toxicity of the fabrication process of KFAMA-based PSCs. Thus, with no specific optimization of the deposition process, and for the maximum possible partial substitution of DMF with NMP and EA solvents, the loss in the power conversion efficiency (PCE) value is only 35% and 18%, respectively, associated with the more structural defects promoted by NMP and EA.

In this paper, the stability of magnesium-doped hydroxyapatite/chitosan (MHC) suspension obtained with the sol-gel approach was evaluated using nondestructive ultrasound measurements. The MHC coatings obtained by the spin-coating technique were characterized before and after immersion for 7 and 14 days, respectively, in Dulbecco's modified eagle medium (DMEM) by scanning electron microscopy, equipped with an EDAX detector. Also, the functional groups present on the MHC coatings surface were analyzed with the aid of attenuated total reflection (ATR) Fourier transform infrared (FTIR) spectroscopy. The surface microstructure was evaluated using two commentary techniques, namely atomic force microscopy (AFM) and metallographic microscopy (MM). The influence of immersion in DMEM on the biological properties was studied with in vitro studies using primary osteoblast and HCT-8 cell lines. Our results revealed that both surface morphology and chemical composition of the MHC coatings allow rapid development of a new apatite layer on their surface after immersion in DMEM. Preliminary in vitro biological studies underlined the noncytotoxic effect of the studied samples on the proliferation of primary osteoblast and HCT-8 cell lines, which makes them a promising candidate for applications in fields such as orthopedics or dentistry. The antifungal assay of the MHC coatings was assessed using Candida albicans ATCC 10231 and their results showed a good inhibitory effect. The coatings made on the basis of the MHC composite could contribute to increasing the degree of success of implants by decreasing the risk of infections and postoperative inflammation.

This article's objective is the synthesis of new composites based on thermoplastic polyurethane (TPU) and TiO2 nanowires (NWs) as free-standing films, highlighting their structural and optical properties. The free-standing TPU-TiO2 NW films were prepared by a wet chemical method accompanied by a thermal treatment at 100 degrees C for 1 h, followed by air-drying for 2 h. X-ray diffraction (XRD) studies indicated that the starting commercial TiO2 NW sample contains TiO2 tetragonal anatase (A), cubic Ti0.91O (C), and orthorhombic Ti2O3 (OR), as well as monoclinic H2Ti3O7 (M). In the presence of TPU, an increase in the ratio between the intensities of the diffraction peaks at 43.4 degrees and 48 degrees belonging to the C and A phases of titanium dioxide, respectively, is reported. The increase in the intensity of the peak at 43.4 degrees is explained to be a consequence of the interaction of TiO2 NWs with PTU, which occurs when the formation of suboxides takes place. The variation in the ratio of the absorbance of the IR bands peaked at 765-771 cm(-1) and 3304-3315 cm(-1) from 4.68 to 4.21 and 3.83 for TPU and the TPU-TiO2 NW composites, respectively, with TiO2 NW concentration equal to 2 wt.% and 17 wt.%, indicated a decrease in the higher-order aggregates of TPU with a simultaneous increase in the hydrogen bonds established between the amide groups of TPU and the oxygen atoms of TiO2 NWs. The decrease in the ratio of the intensity of the Raman lines peaked at 658 cm(-1) and 635 cm(-1), which were assigned to the vibrational modes E-g in TiO2 A and E-g in H2Ti3O7 (ITiO2-A/I-H2Ti3O7), respectively, from 3.45 in TiO2 NWs to 0.94-0.96 in the TPU-TiO2 NW composites, which indicates that the adsorption of TPU onto TiO2 NWs involves an exchange reaction of TPU in the presence of TiO2 NWs, followed by the formation of new hydrogen bonds between the -NH- of the amide group and the oxygen atoms of TixO2x-mn, Ti2O3, and Ti0.91O. Photoluminescence (PL) studies highlighted a gradual decrease in the intensity of the TPU emission band, which is situated in the spectral range 380-650 nm, in the presence of TiO2 NW. After increasing the TiO2 NW concentration in the TPU-TiO2 NW composite mass from 0 wt.% to 2 wt.% and 17 wt.%, respectively, a change in the binding angle of the TPU onto the TiO2 NW surface from 12.6 degrees to 32 degrees and 45.9 degrees, respectively, took place.

Pb(Zr,Ti)O-3 (PZT) is the most common ferroelectric (FE) material widely used in solid-state technology. Despite intense studies of PZT over decades, its intrinsic band structure, electron energy depending on 3D momentum k, is still unknown. Here, Pb(Zr0.2Ti0.8)O-3 using soft-X-ray angle-resolved photoelectron spectroscopy (ARPES) is explored. The enhanced photoelectron escape depth in this photon energy range allows sharp intrinsic definition of the out-of-plane momentum k and thereby of the full 3D band structure. Furthermore, the problem of sample charging due to the inherently insulating nature of PZT is solved by using thin-film PZT samples, where a thickness-induced self-doping results in their heavy doping. For the first time, the soft-X-ray ARPES experiments deliver the intrinsic 3D band structure of PZT as well as the FE-polarization dependent electrostatic potential profile across the PZT film deposited on SrTiO3 and LaxSrMn1-xO3 substrates. The negative charges near the surface, required to stabilize the FE state pointing away from the sample (P+), are identified as oxygen vacancies creating localized in-gap states below the Fermi energy. For the opposite polarization state (P-), the positive charges near the surface are identified as cation vacancies resulting from non-ideal stoichiometry of the PZT film as deduced from quantitative XPS measurements.

Green nanotechnology is a rapidly growing field linked to using the principles of green chemistry to design novel nanomaterials with great potential in environmental and health protection. In this work, metal and semiconducting particles (AuNPs, AgClNPs, ZnO, AuZnO, AgClZnO, and AuAgClZnO) were phytosynthesized through a "green" bottom-up approach, using burdock (Arctium lappa L.) aqueous extract. The morphological (SEM/TEM), structural (XRD, SAED), compositional (EDS), optical (UV-Vis absorption and FTIR spectroscopy), photocatalytic, and bio-properties of the prepared composites were analyzed. The particle size was determined by SEM/TEM and by DLS measurements. The phytoparticles presented high and moderate physical stability, evaluated by zeta potential measurements. The investigation of photocatalytic activity of these composites, using Rhodamine B solutions' degradation under solar light irradiation in the presence of prepared powders, showed different degradation efficiencies. Bioevaluation of the obtained composites revealed the antioxidant and antibacterial properties. The tricomponent system AuAgClZnO showed the best antioxidant activity for capturing ROS and ABTS center dot(+) radicals, and the best biocidal action against Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa. The "green" developed composites can be considered potential adjuvants in biomedical (antioxidant or biocidal agents) or environmental (as antimicrobial agents and catalysts for degradation of water pollutants) applications.

Iron oxide nanoparticles are one of the most promising tools for theranostic applications of pancreatic cancer due to their unique physicochemical and magnetic properties making them suitable for both diagnosis and therapy. Thus, our study aimed to characterize the properties of dextran-coated iron oxide nanoparticles (DIO-NPs) of maghemite (gamma-Fe2O3) type synthesized by co-precipitation and to investigate their effects (low-dose versus high-dose) on pancreatic cancer cells focusing on NP cellular uptake, MR contrast, and toxicological profile. This paper also addressed the modulation of heat shock proteins (HSPs) and p53 protein expression as well as the potential of DIO-NPs for theranostic purposes. DIO-NPs were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), dynamic light scattering analyses (DLS), and zeta potential. Pancreatic cancer cells (PANC-1 cell line) were exposed to different doses of dextran-coated gamma-Fe2O3 NPs (14, 28, 42, 56 mu g/mL) for up to 72 h. The results revealed that DIO-NPs with a hydrodynamic diameter of 16.3 nm produce a significant negative contrast using a 7 T MRI scanner correlated with dose-dependent cellular iron uptake and toxicity levels. We showed that DIO-NPs are biocompatible up to a concentration of 28 mu g/mL (low-dose), while exposure to a concentration of 56 mu g/mL (high-dose) caused a reduction in PANC-1 cell viability to 50% after 72 h by inducing reactive oxygen species (ROS) production, reduced glutathione (GSH) depletion, lipid peroxidation, enhancement of caspase-1 activity, and LDH release. An alteration in Hsp70 and Hsp90 protein expression was also observed. At low doses, these findings provide evidence that DIO-NPs could act as safe platforms in drug delivery, as well as antitumoral and imaging agents for theranostic uses in pancreatic cancer.