Crystallization of Silica Xerogels: A Study by Raman and Fluorescence Spectroscopy

Pure and europium doped silica xerogels were annealed at 1050°C to obtain full densification, and at 1300°C to induce crystallization. Raman spectroscopy, time resolved selective luminescence and lifetime measurements were performed on glassy and crystallized samples. We discuss the differences between the Raman spectra of the xerogel annealed at 1050°C and those of a commercial silica. The typical Raman structures of -crystobalite are evident for the 1300°C annealed samples, but a glassy phase coexists, indicating an incomplete crystallization. Fluorescence measurements give information on the environment of the Eu³⁺ ions in the glassy and crystallized sample.