Publications

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.

Obtaining nanoscale materials has allowed for the miniaturization of components, which has led to the possibility of achieving more efficient devices with faster functions and much lower costs. While hydroxyapatite [HAp, Ca-10(PO4)(6)(OH)(2)] is considered the most widely used material for medical applications in orthopedics, dentistry, and general surgery, the magnesium (Mg) is viewed as a promising biodegradable and biocompatible implant material. Furthermore, Mg is regarded as a strong candidate for developing medical implants due to its biocompatibility and antimicrobial properties against gram-positive and gram-negative bacteria. For this study, magnesium-doped hydroxyapatite (Ca10-xMgx (PO4)(6) (OH)(2), x(Mg) = 0.1), 10MgHAp, suspensions were successfully obtained by an adapted and simple chemical co-precipitation method. The information regarding the stability of the nanosized 10MgHAp particles suspension obtained by zeta-potential analysis were confirmed for the first time by a non-destructive ultrasound-based technique. Structural and morphological studies of synthesized 10MgHAp were conducted by X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy in attenuated total reflectance (ATR) mode and scanning electron microscopy (SEM). The XRD analysis of the 10MgHAp samples confirmed that a single crystalline phase associated to HAp with an average grain size about 93.3 nm was obtained. The FTIR-ATR spectra revealed that the 10MgHAp sample presented broader IR bands with less visible peaks when compared to a well-crystallized pure HAp. The SEM results evidenced uniform MgHAp nanoparticles with spherical shape. The antimicrobial activity of the 10MgHAp suspension against gram-positive strains (Staphylococcus aureus ATCC 25923, Enterococcus faecalis ATCC 29212), gram-negative strains (Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853), as well as a fungal strain (Candida albicans ATCC 90029) were evaluated.

Textile materials can be easily used as a support for the nano-decoration with active particles in order to gain new features such as self-cleaning, antimicrobial efficiency, water repellency, mechanical strength, color change and protection against ultraviolet radiations. In this context, our present research reports the fabrication and characterization (physico-chemical analysis and surface morphology) of cotton fabrics treated with reduced graphene oxide decorated with two types of TiO2 nanoparticles co-doped with 1% iron and nitrogen atoms (TiO2/rGO NPs) and synthesized in different hydrothermal conditions by a simultaneous precipitation of Ti3+ and Fe3+ ions to achieve their uniform distribution or after a sequential precipitation of these two cations for obtaining a higher concentration of iron on the surface of Ti4+ oxyhydroxide. Further, the antimicrobial efficiency of these TiO2/rGO-treated textiles and their influence on human cells were assessed. We demonstrated the successful development of TiO2/rGO coating of cotton fabrics which are harmless for human skin cells and inhibit the growth of Staphylococcus aureus and Enterococcus faecalis. These findings confirm their great potential as novel graphene-based materials for biomedical and photocatalytic applications and this approach could be used for the large-scale fabrication of innovative self-cleaning and antimicrobial textiles.

Novel biomedical composites, based on organically modified vermiculite and montmorillonite with deposited Ca-deficient hydroxyapatite (CDH), were prepared. The monoionic sodium forms of vermiculite and montmorillonite were intercalated with chlorhexidine diacetate (CA). The surfaces of organoclays were used for the precipitation of Ca-deficient hydroxyapatite. The composites with Ca-deficient hydroxyapatite showed very good antibacterial effects, similar to the antimicrobial activity of pure organoclay samples. Better antibacterial activity was shown in the organically modified montmorillonite sample with Ca-deficient hydroxyapatite compared with the vermiculite composite, but, in the case of Staphylococcus aureus, both composites showed the same minimum inhibitory concentration (MIC) value. The antimicrobial effect of composites against bacteria and fungi increased with the time of exposure. The structural characterization of all the prepared materials, performed using X-ray diffraction and FT infrared spectroscopy analysis, detected no changes in the original clay or CDH during the intercalation or precipitation process, therefore we expect the strength of the compounds to be in the original power.

Spectroscopic characteristics of Pr3+ ions doped CNGG and CLNGG single crystals were investigated in order to assess their potential as laser materials for visible emission. The Judd-Ofelt intensity parameters for the f-f transitions of Pr3+ ions were used to determine spectroscopic and laser emission features. The temperature dependence of the absorption spectra for the H-3(4) -> P-3(0) transition was used to highlight the multicenter structure, different Stark levels, hot bands, and also the connection between the vibronic and electronic lines. The presence of electron-phonon interaction was also observed in the emission spectra corresponding to the P-3(0) -> H-3(4) transition under different excitation wavelengths. Based on low temperature absorption and emission spectra, partial energy level diagrams of Pr3+ ions doped in CNGG and CLNGG single crystals were obtained. The emission cross-sections for different transitions of Pr3+ ions were evaluated by the Fuchtbauer-Ladenburg formula. The fluorescence decay curve of the D-1(2) level was measured under selective excitation at different concentrations and temperatures. The concentration quenching process for the D-1(2) state was also studied. (C) 2019 Elsevier B.V. All rights reserved.

Multiple nonvolatile and well-separated capacitive states can be obtained in a two-terminal ferroelectric capacitor setup by fine tuning the polarization switching process. This approach allows for the implementation of memcomputing (same platform for storage and computing) capable ferroelectric structures. Digital and analog storage modes are exemplified in this work together with an algorithm for simple binary computation functions such as OR/NOR and AND/NAND for data processing on the same device. Results are obtained by controlling the polarization switching process in ferroelectric multi-layers such as Pb (Zr0.2Ti0.8)O-3/SrTiO3/Pb (Zr0.2Ti0.8)O-3 and Pb (Zr0.2Ti0.8)O-3/BaTiO3/Pb (Zr0.2Ti0.8)O-3. Besides memcomputing, these results can be used for nondestructive capacitive reading of information in simple ferroelectric capacitors or can open the way toward applications such as neuromorphic and chaotic circuits.

The present investigation deals with the development, characterization and application of nano-structured Pd doped Ni electrodes (Pd@Ni), which uses the electrochemical properties of Pd in synergy with the magnetic properties of Ni for biosensors development. The Pd@Ni electrodes have been characterized by X-ray diffraction, scanning electron microscopy with energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. It has been shown that palladium presented spherical assemblies ranging 150-200 nm medium diameter size that covers large areas of the electrode surface while metallic nickel, which confers magnetic properties, showed a uniform granular structure with sizes between 20 and 50 nm. Cyclic voltammetry and electrochemical impedance spectroscopy were performed to understand the electrochemical process at the Pd@Ni electrodes in neutral media. The Pd@Ni electrodes were applied for the electrochemical detection of H2O2. Finally, Ni nanoparticles (NiNP) functionalized with the model enzyme glucose oxidase (GOx-NiNP) have been attached to the Pd@Ni electrode solely through magnetic interactions, and the obtained GOx-NiNP/Pd@Ni biosensor applied for glucose determination in aqueous solutions by fixed potential amperometry at -0.05 V (vs Ag/AgCl) with reduced interferences. (C) 2019 Elsevier Ltd. All rights reserved.

Adsorption processes of 1,4-phenylene diisothiocyanate (PDITC) on two new platforms of the type graphene oxide (GO) sheets and GO layers functionalization with polydiphenylamine (PDPA) are studied by Raman scattering and photoluminescence (PL). An interaction in solid state phase of the two constituents, i.e. PDITC and GO sheets, and a deposition of PDITC onto the PDPA functionalized GO layers, respectively, by the drop casting method, were performed. In the first case, it is shown that interaction in solid state phase of GO with PDITC leads to an intercalation of the organic compound between GO sheets simultaneously with the appearance of the o-thiocarbamate groups, that induces: (i) an enhancement of the PDITC Raman lines situated in the 400-800 and 1000-1300 cm(-1) spectral ranges, (ii) a change in the ratio between the relative intensities of the two Raman lines peaked at 1585 and 1602 cm(-1) accompanied by an up-shift in the case of the second line and (iii) a down-shift of the PDTIC PL band from 502 to 491 nm. Using cyclic voltammetry, an electrochemical functionalization of the GO layers with PDPA doped with H3PMo12O40 heteropolyanions takes place, as demonstrated by Raman scattering and FTIR spectroscopy. The presence of the amine groups in the molecular structure of the doped PDPA functionalized GO layers induces a chemical adsorption of PDITC on this platform, when the thiourea groups appear simultaneously with o-thiocarbamate groups. A chemical mechanism is proposed to take place at the interface of the GO sheets and the doped PDPA functionalized GO layers, respectively, with PDITC.

A carbon-based layer was deposited by spraying on top of a ferroelectric layer grown by sol-gel on Si (001) substrate and its properties as electrode and absorber for pyroelectric detection were tested. It was found that the electric properties of the ferroelectric capacitor with top carbon-based sprayed electrode (CBSE) are comparable with those of the capacitors with standard top SrRuO3 (SRO)/Au electrode. Pyroelectric measurements show that the pyroelectric signal recorded on ferroelectric capacitors with top CBSE electrode is 2.5 times greater than for top SRO/Au electrode for low frequency range. The value of the pyroelectric coefficient was estimated to 9.73.10(-4) C/m(2)K for CBSE electrodes and 3.36.10(-4) C/m(2)K for SRO/Au respectively. The fabrication process of CBSE is of low cost, easy to implement and with high throughput making it attractive for manufacturing various devices like pyroelectric detector, thermal imaging, solar cells, etc.

Electrodes constituted by nitrogen-doped reduced graphene oxide (NrGO) in combination with NiO nanostructures were fabricated by means of reactive inverse matrix assisted pulsed laser evaporation technique. The structure-composition of the electrode composites was tailored by laser-inducing chemical reactions of graphene oxide (GO) flakes with different precursor molecules (citric acid, ascorbic acid and imidazole) during GO deposition. Structural characterizations reveal the formation of wrinkles and nanoholes in the NrGO sheets, besides their coating with NiO nanostructures. Compositional studies disclose that imidazole precursor promotes the synthesis of NrGO with the largest degree of reduction and nitrogen doping (mainly with graphitic and pyridinic N). Electrochemical analyses of the obtained electrodes reveal that NiO nanostructures increase surface charge storage processes (double layer - pseudocapacitive) over diffusive ones, being the imidazole-based electrodes the ones exhibiting the best performance (up to 114 F cm(-3) at 10 mV s(-1)). Symmetric and asymmetric electro-chemical capacitors were also fabricated showing excellent robustness over 10,000 charge-discharge cycles at high specific currents.