Publications

Europium doped hydroxyapatite (Eu:HAp) nanocristalline powders was synthesized by co-precipitation method by setting the atomic ratio of Eu/[Eu + Ca] at 0% and 2% and [Ca+Eu] /P at 1.67. The structural properties were characterized by X-ray diffraction (XRD). Nitrogen adsorption-desorption isotherms were obtained on different samples using BET method. The X-ray diffraction analysis revealed that hydroxyapatite is the unique crystalline constituent of all the samples, indicating that Eu has been successfully inserted into the HAp lattice. Based on N-2 adsorption-desorption isotherms investigation, the pore size, surface area and pore volume of europium doped hydroxyapatite are 16.57 nm, 115.06 m(2)/g and 0.48 cm(3)/g.

Arrays of multisegment Pd/(Zn,Cu)O:Mn/Pd submicron wires have been grown electrochemically into the pores of nuclear track polycarbonate membranes. Their transport properties were investigated, by measuring current-voltage (I-V) characteristics in a temperature range from 300 K down to 40 K. I-V characteristics of Pd/(Zn,Cu)O:Mn/Pd wires exhibited a symmetric, non-linear shape on applied bias voltage ranging from -20 V to +20V. The ohmic region corresponds to polarization voltage under 3.5V. Comparatively, I-V characteristics of Pd/ZnO/Pd array of wires with diameter about 500 nm are linear in the entire range of applied voltages (-20 V to +20V).

A multi-purpose gas-flow proportional counter for surface Mossbauer spectroscopy is described. The main improvements obtained are: the height of the detection volume can be changed in large limits from 1 to 38 mm, the detection volume can be symmetrical or not in respect with anode plan, the anode changing is easily and different anode configuration can be used. It is suitable for studies with (57)Fe, (119)Sn and (151)Eu isotopes. The performances of the detector are presented.

The electrical behavior of multi-walled carbon nanotube network embedded in amorphous silicon nitride is studied by measuring the voltage and temperature dependences of the current. The microstructure of the network is investigated by cross-sectional transmission electron microscopy. The multi-walled carbon nanotube network has an uniform spatial extension in the silicon nitride matrix. The current-voltage and resistance-temperature characteristics are both linear, proving the metallic behavior of the network. The I-V curves present oscillations that are further analyzed by computing the conductance-voltage characteristics. The conductance presents minima and maxima that appear at the same voltage for both bias polarities, at both 20 and 298 K, and that are not periodic. These oscillations are interpreted as due to percolation processes. The voltage percolation thresholds are identified with the conductance minima.

Doped ceria powders, Ce-0.8 Ln(0.2)O(2-x) (Ln = Gd3+, Sm3+ and Yb3+) were sintered to nearly full density by Spark Plasma Sintering at 1100 and 1200 degrees C. The starting powders were obtained via a sol-gel method and had nanometric dimensions: 26.4 nm (Gd), 19.3 nm (Sm) and 31.4 nm (Yb). Samples characterization was performed by SEM, TEM and XRD to determine their structural and microstructural characteristics. The ionic conductivities of the sintered samples were determined by impedance measurements. The influence of the chemical composition, sintering temperature and microstructural characteristics on the total ionic conductivity were evaluated and discussed.

For the first time we presented the preliminary results of biocompatibility studies on bioceramic hydroxyapatite powders doped with europium Ca10-xEux(PO4)(6)(OH)(2), with 0.01 <= x(Eu) <= 0.2 prepared at low temperature by a simple coprecipitation approach. The X-ray diffraction (XRD) studies revealed the characteristic peaks of hydroxyapatite in each sample. No evidence for additional crystalline phases was found, proving the complete substitution of Eu in the HAp lattice in the whole range of concentrations. The scanning electron microscopy (SEM) observations suggest that these materials present a little different morphology, which reveals a homogeneous aspect of the synthesized particles for all samples. The PL investigations shown the PL intensity changed considerably by varying the x(Eu). The value of x(Eu) in the hydroxyapatite formula has almost no effect on the wavelength of emission peaks. In order to test Hap_Eu biocompatibility, the effect of europium substituted hydroxyapatite nanocristalline powders with different x(Eu) on cell viability and proliferation of HEK293 cell line were evaluated. The in vitro investigation showed no significant decrease of viability of HEK293 cell line and low levels of intracellular lipid peroxidation in the Hap_Eu treated cells. In conclusion, the results suggest that Eu doped HAp has low toxicity and exhibit a good biocompatibility.

The photoluminescence (PL) of two types of poly (N-vinyl-carbazole)(PVK)/carbon nanotubes (CN) composites, prepared by chemical and electrochemical method, has been investigated. In comparison with the pure PVK, the chemically prepared PVK/NC sample shows a significant PL quenching and a shorter decay time. For the samples prepared electrochemically, PL increases in intensity, red shifts and gets longer decay time with the increase of voltammetric cycles number. In addition, the latter shows a change in emission from high-energy excimer to low-energy excimer after a treatment with NH(4)OH.

Nowadays, porphyrin derivatives are extensively used as analytical reagents. This work put the basis for a rapid, simple and inexpensive method developed for pH determination. It was demonstrated the potential for a water soluble metalloporphyrin, 5,10,15,20-tetrakis(N-methyl-4-pyridyl) porphyrin-Zn(II) tetrachloride (Zn-TNMPyP) to be a potential optical pH sensor in the 5.5-10.5 domain. Monitoring of the variations in the absorption spectra of the Zn-TNMPyP, both regarding the Soret and the Q(0,1) band, generated by the exposure to different base concentrations allowed us to notice the linearity of the response at different pH values.

The attractive properties of Yttria doped ceria, particularly the structural and material properties, have led to vast research efforts to investigate and develop such materials. One of the main applications of this ceramic is in the solid oxides fuel cells for intermediate temperatures IT-SOFC. The aim of this paper is the preparation and characterization of Y doped Ceria - low Y doped alpha-Al2O3, a new composite for IT-SOFC. (10 mol %) Y : CeO2 and (150 ppm) Y : alpha - Al2O3 - composite were obtained by sol-gel or mechanical route for 10YSC, mechanical route for 150 Y : alpha - Al2O3. Grain shapes, grain size distributions and the mean grain value were determined by SEM, EDX and statistical investigations.

The synthesis of a new garnet, Er3Li0.275Nb0.275Ga4.45O12 (ErLNGG), by solid-state reaction, is reported. A comparison of the fluorescence spectra of Er3+ in ErLNGG and in Er-doped (5 at. %) Calcium Lithium Niobium Gallium Garnet (CLNGG) suggests an ordering of the partially disordered CLNGG when Ca2+ ions are completely substituted by Er3+ ions.