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Ce3+-doped boro, phospho and borophosphosilicate monolithic glasses (BSG, PSG and BPSG) were prepared by sol-gel method. The inclusion of the glass formers P and B in silica lowered the tendency of rare earth (RE) to segregate as CeO2 with respect to pure SiO2 matrix (SG). In PSG and BPSG, Ce3+ co-ordination to P=O groups was responsible for the inhibition of both CeO2 segregation and oxidation of isolated Ce3+ ions to Ce4+. The better ion dispersion in the host matrix and the stabilization of Ce3+ oxidation state improved PSG and BPSG luminescence properties with respect to BSG and SG.
Silica-copper molybdates prepared by sol-gel and impregnation methods were tested as catalysts in the oxidation of propene at 400°C, both in a pulse and in a flow reactor. Their catalytic activity is connected to their structural features, as revealed by electron paramagnetic resonance (EPR) and X-ray diffraction (XRD) characterization.
SnO2, Ru/SnO2 and Pt/SnO2 were prepared by sol-gel condensation method. Ru/SnO2 was also obtained by supporting the metal on SnO2 xerogel. The reactivity of these materials towards CO and air, studied by Electron Paramagnetic Resonance spectroscopy (EPR), suggests that the electron transfer processes at the oxide surface are favored by the presence of the metal, in the order Pt > Ru ion-exchanged > Ru-supported. A rationale was given for the differences and for the choice of a material suitable to high sensitivity gas sensors.
Sn centers are point defects easily formed by X-ray irradiation of Sn-doped silica. Point defects are a tool for assessing the substitutional character of the dopant in Sn-doped SiO2 glasses with different Sn content (SnO2/SiO2 ratio from 0.01 to 10.0 % w/w) and prepared by two sol-gel methods differing in tin precursors (tin tetraterbutoxide and tin dibutyldiacetate). The former method produced transparent crack-free monolithic glasses of Sn-doped silica with maximum tin content of 0.1 % (SnO2/SiO2 % w/w). The latter method is more efficient and produced transparent glasses with a tin content of 1%.
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