Evidences of Rare-Earth Nanophases Embedded in Silica Using Vibrational Spectroscopy

Transmission electron microscopy, Raman scattering, Fourier transform infrared spectroscopy, and radio-luminescence are employed to investigate rare-earth (RE) incorporation and aggregate formation in silica glasses prepared by the Sol-Gel method and doped with Ce³⁺, or Tb³⁺, Gd³⁺, Yb³⁺ with concentrations up to several mol%. The results demonstrate that rare-earth aggregates with a mean diameter extending up to several tens of nanometers occur, further increasing their size after post-densification high temperature treatments. Rare-earth segregation causes a reduction of the OH content of glasses. Nanoclusters are amorphous, possibly close to a (RE)₂SiO₅ stoichiometry. Room temperature radio-luminescence measurements reveal that the emission spectra are dominated by RE³⁺ emissions and no bands due to silica matrix defects are detected.