National Institute Of Materials Physics - Romania

Un-doped and Tb3+-doped calcium and strontium aluminates (CaAl2O4, CaAl2O4:Tb3+, SrAl2O4, SrAl2O4: Tb3+) were synthesized by a new soft chemical method the precursor route via the thermal decomposition of tartarate compounds. The complex precursors have been characterized by elemental chemical analysis, infrared spectroScopy (IR), luminescence spectroscopy and thermal analysis. X-ray diffraction (XRD), scanning electron microscopy (SEM), IR and Raman spectroscopy (RS) were used for the structural and morphological characterization of un-doped and doped alkaline-earth aluminate powders. Photoluminescence (PL) and Thermoluminescence (TL) properties of the aluminates were also investigated. The XRD patterns confirmed the formation of low-temperature structures: hexagonal structure for CaAl2O4 and monoclinic structure for SrAl2O4, with average crystallite size of 64 nm and 46 nm for CaAl2O4 and SrAl2O4, respectively. Microstructural analysis by SEM showed the homogeneous microstructure and fine particle size of the powder obtained by precursor method. (C) 2016 Elsevier Ltd. All rights reserved.

Synthesis and characterization of four new Ni(II) complexes with mixed ligands have been reported in the present paper. As interest ligands, acrylate (acr) ion together with one N-donor heterocyclic ligand, namely benzimidazole (HBzIm), 2-methylbenzimidazole (2-MeBzIm), 5-methylbenzimidazole (5-MeBzIm) or 5,6-dimethylbenzimidazole (5,6-Me(2)BzIm), was chosen. The syntheses afforded the complexes formulated as [Ni(HBzIm)(2)(acr)(2)(H2O)]center dot 3H(2)O (1), [Ni(2-MeBzIm)(2)(acr)(2)(H2O)]center dot 1.5H(2)O (2), [Ni(5-MeBzIm)(2)(acr)(2)(H2O)] (3) and [Ni(5,6-Me(2)BzIm)(2)(acr)(2)] (4). Complexes (1) and (2) contain crystallization water molecules and coordinated water molecules, both their nature and presence being confirmed on the basis of IR spectra and thermal analysis. In contrast to above-mentioned complexes, (3) contains only coordinated water molecule, while (4) is an anhydrous compound. Based on electronic spectra and magnetic measurements, a distorted octahedral stereochemistry was proposed for all Ni(II) complexes. Acrylate ions act both as unidentate and chelate ligands in complexes (1)-(3), while in complex (4) act only as chelate ligands. All used N-donor ligands function as monodentate in all Ni(II) complexes. Biological properties of complexes (1)-(4) were evaluated against several Gram(+), Gram(-) bacterial strains and against fungus Candida albicans.

Photoactive europium doped titanium dioxide (Eu: TiO2) thin films were grown by a matrix assisted pulsed laser evaporation technique. TiO2 and Eu cation-adsorbed TiO2 nanoparticles (NPs) sols were used as starting materials. The sols were synthesized by a colloidal sol-gel route. In order to obtain solid targets, the sols were cooled down until solidification in liquid nitrogen. The irradiation of the solid targets was performed in a controlled oxygen atmosphere using an UV KrF* (lambda = 248 nm, tau(FWHM) nu 25 ns, n = 10 Hz) excimer laser source. The NPs were transferred and deposited onto solid substrates placed in the front of the frozen targets, forming continuous thin films. The as-grown undoped and Eu: TiO2 thin films were submitted to post-deposition thermal treatments. The surface morphology, crystalline structure, and chemical composition of the thin films were characterized by field emission scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. Functional optical properties of the films were investigated by UV-VIS-NIR spectroscopy, spectroscopic ellipsometry, and photoluminescence as a function of dopant concentration in the TiO2 host and annealing temperature. A direct correlation was established between the processing conditions, films structure, chemical composition and oxidation states studied both at the top surface and in-depth as well as their functional, optical properties. Eu doping induces a blue-shift of the absorption edge with respect to the as-grown samples. Under visible light excitation (lambda = 488 nm, emitted by an Ar+ laser source), the Eu: TiO2 samples show characteristic photoluminescence corresponding to the D-5(0) -> F-7(i) (i = 0, 1, 2, 3, 4) transitions of Eu+ ions in the visible spectral range. The samples treated at the highest annealing temperature are characterized by strong photoluminescence emission, high transmittance in the VIS-NIR spectral regions, and high refractive index.

The photosensing properties related to the structure of GeSi/TiO2 multilayers prepared under different conditions are studied. TiO2 cap/(GeSi/TiO2)(2) multilayers (ML) were deposited by magnetron sputtering (MS) and annealed by rapid thermal annealing. Trilayers of TiO2 cap/GeSi/TiO2 (TL) were also deposited using reactive high power impulse MS (HiPIMS) for TiO2 layers and dc MS for the GeSi layer. For TL samples a two-step annealing was employed, one before and the second after depositing TiO2 cap. Structure and morphology characterization (X-ray diffraction, scanning and transmission electron microscopy) was carried out and photocurrent measurements (voltage dependences, spectral curves) were performed. The annealed ML samples are formed of GeSi NCs with 5 - 10 nm sizes, while in the annealed TL samples, the GeSi NCs are larger (20 - 30 nm). These morphologies determine the multilayers photosensing properties in VIS-NIR of ML structures and in UV in TL ones, respectively.

SnO2 loaded with 1 wt.% NiO based gas sensors, have been tested under humid background towards different H2S concentrations when operated at 350 degrees C. Knowing that water dissociation takes place, leading to the formation of strongly bonded surface hydroxyl groups, usually hindering the subsequent gas detection, it is of highly importance to understand the role of NiO as "OH groups trapper" element. By using complementary phenomenological investigations (simultaneous electrical resistance and work function measurements) we could emphasize the role of loading element in mitigating the water effects, further reflected through the different H2S interaction mechanisms. As such, the exposure of the SnO2 - 1 wt.% NiO sensors to different relative humidity levels was mirrored through a decrease in surface band bending due to the water donor effect and to a minor increase in the electronic affinity explained by the low adsorption of surface OH groups.

Investigations on antenna array for 5.8 GHz frequency band applications are presented in this paper. In order to enhance the characteristics of the dielectric resonator antenna elements, a pair of resonators with different sizes and dielectric constants is used. The antenna elements are connected to four daughter-boards of Universal Software Radio Peripherals, which perform the signal processing required by the sources detection and beamforming.

Cobalt ferrites nanoparticles (CoFe2O4) were synthesized through self-combustion method using aqueous extracts of ginger root and cardamom seeds. X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared spectroscopy (IR) and Mossbauer spectroscopy were used for the characterization of the cobalt ferrite nanoparticles. X-ray diffraction patterns indicated the formation of the cubic phase CoFe2O4. SEM micrographs revealed different morphological features of obtained cobalt ferrites. The Mossbauer parameters together with the inversion parameter and the cationic distribution were obtained from Mossbauer spectra recorded at room temperature.