Publications

We investigate the down- and up-conversion properties of Er (0.3, 1 and 3%)-CeO2 and Er(1%)Yb(20%)-CeO2 nanoparticles by use of ns pulsed monochromatic excitation. The emission spectra were recorded in the visible to near-infrared range (500-1100 nm) under ultraviolet, visible (490 and 650 nm) and near infrared (790, 971/977 and 1470 nm) up-conversion excitations as well as X-ray excitation. The structural properties were characterized by X-ray diffraction, Raman, Diffuse Reflectance UV/Vis and Diffuse Reflectance Fourier Transform Infrared spectroscopies. The role of CeO2 charge transfer band as a level selective antenna sensitizer, the dopant induced oxygen vacancies and the effect of Er concentration on the overall emission properties are highlighted. The mechanisms involved in the up-conversion emission in Er-CeO2 and Er,Yb-CeO2 are analysed in terms of up-conversion excitation spectra, up-conversion emission decays and evolution of the red to green emission ratio with Er concentration and delay after the laser pulse. Our findings are also discussed in the context of a comprehensive literature survey regarding the actual stage of research on the luminescence of Er and Er,Yb doped CeO2 and their possible applications. (C) 2017 Elsevier B.V. All rights reserved.

A comparative study of morpho-structural, magnetic and magneto-transport properties of two Fe-Au granular films with different concentrations of Fe nanoclusters of almost similar size is reported. Different organizations of the Fe clusters, i.e. in lamellar-like or random-like configuration, were obtained by varying the amount of Fe in the Fe-Au films. The specific magnetic behaviour was investigated with respect to local structure and morpho-structural aspects by combining magneto-optic Kerr effect and superconducting quantum interference device magnetometry, Fe-57 conversion electron Mossbauer spectroscopy and a wide range of electron microscopy techniques. A strong in-plane magnetic texture with uniaxial anisotropy was observed in the case of the lamellar-like organization of the clusters (specific to the Fe-Au film with higher Fe concentration) whereas a superparamagnetic behaviour was evidenced in the case of random distribution of the clusters (specific to the Fe-Au film with lower Fe concentration), despite the similar average size of the clusters in the two samples. Specific magnetoresistance effects were investigated with respect to both the involved magnetic configurations and magnetic interactions of the Fe clusters.

The synthesis and physicochemical characterization of riboflavin (RF) loaded Myrj52-silver nanoparticles (SNPs) were performed and their cytotoxic properties were evaluated. Transmission electron microscopy analysis showed the formation of colloidal spherical SNPs with an average size of similar to 12 nm. The structure, stability, dynamics and conformation of human serum albumin (HSA) binding RF on SNPs have been studied. The influence of RF on the secondary structure of HSA in the presence of SNPs showed a predominant alpha-helix structure (61.7%). No changes induced by RF binding to HSA were observed. The cytotoxicity of RF and RF-HSA loaded Myrj52-SNPs was evaluated in vitro using the Neutral Red assay and cell morphology observations in a culture of L929 fibroblast cells. The results have relevance with regard to the RF loaded Myrj52-SNP formulation for pharmaceuticals.

Local symmetry distortion by Li addition is acknowledged as an effective strategy for enhancing the luminescence of lanthanide (Ln) doped into a wide range of lattice hosts. Despite extensive literature, direct evidence that supports Li-induced modification of the local crystal-field at the Ln sites is still missing. Herein, we show that the emission enhancement by Li addition in Ln,Li-Y2O3 is due to improved crystallization and not to local structure distortion. Our approach is based on the premise that any distortion/lowering of the local symmetry would reflect into the alteration of the emission shapes and shortening of the emission decays. To this aim, we have extensively investigated the evolution with Li addition and calcination temperature of down (optical and X-ray induced) and up-conversion (UPC) emission of Ln-Y2O3 measured across the visible to near-infrared range. First, a center to center (corresponding to Ln in the C-2 and S-6/C-3i sites of the cubic Y2O3 lattice) as well as global comparison of the emission properties of Li free and Li codoped Y2O3 are presented by use of Eu, Sm, Tb and Dy as local probes in the visible range. Next, the effect of Li on the up-conversion emission of Er-Y2O3 is analyzed in terms of UPC pathways, emission shape and intensity, decays and excitation spectra. It is concluded that Li addition does not change either the local structure around C-2 or S-6 Ln centers or the relative contribution of these. Moreover, it is found that the effects of Li doping on the emission properties of Ln-Y2O3 are like extending the calcination temperature of Li-free Ln-Y2O3 from 800 degrees C to similar to 1000-1100 degrees C. Additionally, a relatively intense 1500 to 980 nm UPC emission is evidenced for the first time for Er-Y2O3, while a relatively intense "emission around 1500 nm was measured under X-ray excitation. Taken together, our findings highlight the need for revisiting the traditional optimization strategy based on Li modification but also the promise of Er-Y2O3 nanoparticles for optical/X-ray applications in the near-infrared range.

The structural electronic and magnetic properties of CoFeZrSi material with tetragonal and triclinic distorted primitive cell were investigated within the Density Functional Theory (DFT) framework. Half metallic soft ferromagnetism with high Curie temperature was evidenced in this quaternary compound which crystallizes optimally in the cubic LiMgPdSn type structure. The material preserves the half metallic characteristic when the cubic primitive cell is tetragonally deformed or when the unit cell volume increases or decreases due to external applied pressure. On contrary, the energy band gap, typical for half-metals, located in the minority spin channel disappears when the unit cell is triclinic deformed, e.g. under interfacial distortions. The material exhibits metallic behavior and the total magnetic moment increases from the integral 1 mu B/f.u., calculated for cubic and tetragonal unit cells, up to 3.25 mu B/f.u. for triclinic structure with a = b = c and alpha = beta = 90 degrees gamma = 89 degrees. (C) 2017 Elsevier B.V. All rights reserved.

Nano-sized lanthanum doped barium titanate Ba1-xLaxTiO3 (0.00 <= x <= 0.08) powders were prepared by sol-gel method. These powders with perovskite BaTiO3 cubic single phase structure, obtained after calcinations of gels precursors at 1100 degrees C, 3 h in air, were pressed and sintered by spark plasma technique in order to obtain dense ceramics. The optimal sintering temperatures used for Ba1-xLaxTiO3 powders were dependent on lanthanum amount added to barium titanate and decrease from 1300 degrees C to 1160 degrees C when the La concentration increases from 0 to 8 at.% La. An additional annealing treatment was made in air at 900 degrees C for all the sintered pellets for oxidize and remove the contaminant graphite which migrated in ceramics from the graphite die during the sintering process. The effect of lanthanum concentration on the densification behavior, structure, microstructure, photoluminescence and dielectric properties of the Ba1-xLaxTiO3 ceramics was investigated in this work. The results shown that as the lanthanum content increases, the grain size of the powders and ceramics increases accompanied by decrease of density of the samples. Also, increase of La amount inserted in BaTiO3 lattice leads to significant decrease of the dielectric losses and Curie temperature and, increase of dielectric permittivity but the luminescence properties seem to be less affected. (C) 2017 Elsevier B. V. All rights reserved.

Development of new sensitive materials by different synthesis routes in order to emphasize the sensing properties for hazardous H2S detection is one of a nowadays challenge in the field of gas sensors. In this study we obtained mesoporous SnO2-CuWO4 with selective sensitivity to H2S by an inexpensive synthesis route with low environmental pollution level, using tripropylamine (TPA) as template and polyvinylpyrrolidone (PVP) as dispersant/stabilizer. In order to bring insights about the intrinsic properties, the powders were characterized by means of a variety of complementary techniques such as: X-Ray Diffraction, XRD; Transmission Electron Microscopy, TEM; High Resolution TEM, HRTEM; Raman Spectroscopy, RS; Porosity Analysis by N-2 adsorption/desorption, BET; Scanning Electron Microscopy, SEM and X-ray Photoelectron Spectroscopy, XPS. The sensors were fabricated by powders deposition via screen printing technique onto planar commercial Al2O3 substrates. The sensor signals towards H2S exposure at low operating temperature (100 degrees C) reaches values from 10(5) (for SnWCu600) to 10(6) (for SnWCu800) over the full range of concentrations (5-30 ppm). The recovery processes were induced by a short temperature trigger of 500 degrees C. The selective sensitivity was underlined with respect to the H2S, relative to other potential pollutants and relative humidity (10-70% RH). (C) 2017 Elsevier B.V. All rights reserved.

We report on the fabrication of silicon-reinforced carbon (C: Si) structures by combinatorial pulsed laser deposition to search for the best design for a new generation of multi-functional coated implants. The synthesized films were characterized from the morphological, structural, compositional, mechanical and microbiological points of view. Scanning electron microscopy revealed the presence, on top of the deposited layers, of spheroid particulates with sizes in the micron range. No microcracks or delaminations were observed. Energy dispersive x-ray spectroscopy and grazing incidence x-ray diffraction pointed to the existence of aC to Si compositional gradient from one end of the film to the other. Raman investigation revealed a relatively high sp(3) hybridization of up to 80% at 40-48 mm a part from the edge with higher Ccontent. Si addition was demonstrated to significantly increase C: Si film bonding to the substrate, with values above the ISO threshold for coatings to be used in high-loading biomedical applications. Surface energy studies pointed to an increase in the hydrophilic character of the deposited structures along with Si content up to 52 m Nm(-1'). In certain cases, the Si-reinforced Ccoatings elicited an antimicrobial biofilm action. The presence of Si was proven to be benign to HEp-2 cells of human origin, without interfering with their cellular cycle. On this basis, reliable C: Si structures with good adherence to the substrate and high efficiency against microbial biofilms can be developed for implant coatings and other advanced medical devices.

Hysteretic effects are investigated in perovskite solar cells in the standard FTO/TiO2/CH3NH3PbI3-xClx/spiro-OMeTAD/Au configuration. We report normal (NH) and inverted hysteresis (IH) in the J-V characteristics occurring for the same device structure, and the behavior strictly depends on the prepoling bias. NH typically appears at prepoling biases larger than the open circuit bias, while pronounced IH occurs for negative bias prepoling. The transition from NH to IH is marked by an intermediate mixed hysteresis behavior characterized by a crossing point in the J-V characteristics. The measured J-V characteristics are explained quantitatively by the dynamic electrical model. Furthermore, the influence of the bias scan rate on the NH/IH hysteresis is discussed based on the time evolution of the accumulated ionic and electronic polarization charge at the interfaces. Introducing a three-step measurement protocol, which includes stabilization, prepoling, and measurement, we put forward the difficulties and possible solutions for a correct photoconversion efficiency evaluation.

Bi3+, Pb2+ and Bi3+-Pb2+-containing aluminophosphate glasses were obtained by unconventional wet method, the molar formula of the glasses being: i) 58LiPO(3), 29Al(PO3)(3), 10Ba(PO3)(2), 3Bi(2)O(3); ii) 58LiPO(3), 29Al(PO3)(3), 10Ba(PO3)(2), 3PbO and iii) 6LiPO(3), 3Al(PO3)(3), 1Ba(PO3)(2), 10Bi(PO3)(3), 80Pb(PO3)(2). The glass samples were investigated to determine the density, the thermal expansion coefficients and the chemical stability. The magnetic measurements for Bi and Pb-single doped glasses revealed a diamagnetic behavior and those of Bi-Pb-containing glass disclosed a diamagnetic behavior superposed a small paramagnetic contribution, observed in low magnetic fields that can be attributed to the impurities presented in the matrix. The Verdet constant for the analyzed glasses appeared to have positive values proving a diamagnetic behavior of the investigated material. (C) 2016 Published by Elsevier B.V.