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The aim of this work is to highlight the correlation between treatment conditions, composition, and structure of reduced zinc oxide (ZnO:Zn) with optical and radioluminescence properties for the production of high yield scintillating powders. Purchased zinc oxide (ZnO) powders (≈0.35 ± 0.15 μm) were thermally reduced in Ar/H2 (3%) atmosphere at temperatures ranging between 600 (≈0.40 ± 0.17 μm) and 1000 °C (≈6.4 ± 1.6 μm), obtaining ZnO:Zn powders. The reduction degree, evaluated through energy dispersive spectroscopy, showed a linear increase from 0% up to 20% (800 °C sample), reaching a plateau condition at about 25% for the highest treatment temperatures (1000 °C sample). Structural analysis highlighted the existence of a threshold temperature, previously reported in the literature, around 800 °C, beyond which (i) the grain size remarkably increases, (ii) the shape changes from hexagonal to round-shaped, and (iii) the intensity of electron spin resonance (ESR)-active defects at g = 1.9596 decreases for a new resonance at g = 2.0105. Additionally, a substantial variation, from 5.63 ± 0.02 down to 5.2 ± 0.1 g/cm3, of the skeletal density and a slight contraction of the optical bandgap are observed. Unlike the structural properties, PL and x-ray radioluminescence showed a continuous increase of the green emission intensity, associated with ESR-active ionized oxygen vacancies and ESR non-active recombination centers, and of the PL defective lifetimes (33 ns < τfast < 88 ns, 395 ns < τslow < 930 ns). [ABSTRACT FROM AUTHOR]

Research describing nucleation and crystallization in oxide glasses is presented. In particular the size distribution and structure of nanoparticles in the glass matrix is investigated.

This work is aimed at a deeper understanding of the polarity-sensitive electro-optical response observed in a liquid crystal (LC) cell with asymmetric insertion of thin films of TiO[SUB2]-V[SUB2]O[SUB5] having a Ti/V atomic ratio of 1/1, prepared by sol-gel synthesis on a transparent indium tin oxide substrate. After preliminary structural characterization of the films, the electro-optical response of the liquid crystal cells containing a TiO[SUB2]-V[SUB2]O[SUB5] layer has been analyzed. The voltage thresholds of the Freedericksz transition are increased or decreased for anodic or the cathodic polarization, respectively, of the TiO[SUB2]-V[SUB2]O[SUB5] film. In such a way a polarity-sensitive electro-optical response is generated that has the same frequency as the field applied. Impedance and cyclic voltammetry measurements were performed on liquid crystal cells having TiO[SUB2]-V[SUB2]O[SUB5] films inserted as the electrode, for as-deposited films as well as for films annealed at 400 °C. The LC cell containing thermally annealed Ti/V 1/1 film showed a rectified square wave response instead of the usual impulsive one, quadratic versus electric field. On the contrary, the LC cell containing as-deposited Ti/V 1/1 film exhibits more complex electro-optical behavior with a weak asymmetric response. All the measurements suggest that charge redistribution of the ions, always present in the films, occurs during the intercalation-deintercalation processes induced by the voltage applied, and this is responsible for changes of the effective electric field that act on the liquid crystal layer. [ABSTRACT FROM AUTHOR]

A multitechnique approach, consisting of x-ray diffraction, differential thermal analysis, low frequency Raman scattering from the acoustic vibrations of nanoclusters, and transmission electron microscopy associated with selected area diffraction, has been used to study the nucleation and crystallization processes in SiO[sub 2]–Ga[sub 2]O[sub 3]–K[sub 2]O glasses. The specific aim was to determine the structure and the size distribution of nanoparticles embedded in the glass matrix. It has been found that nearly spherical nanocrystals of β-Ga[sub 2]O[sub 3], with a size of ∼2–3 nm, nucleate during thermal treatments at 900 °C. Crystallization was observed after annealing at higher temperature. The amount of the crystalline phase and the mean size of the nanocrystals increased with heat treatment, time and temperature. β-Ga[sub 2]O[sub 3] was the only crystalline phase to appear in all glass samples. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]