Abstract

Silica glasses with substitutional Sn-doping or with dispersion of SnO₂ nanoclusters were prepared by the sol–gel method. The occurrence of SnO₂ clustering was investigated by optical absorption, Raman scattering and electron paramagnetic resonance spectroscopies, varying both the tin concentration and the densification temperature of Sn-doped silica xerogels. The 3.7 eV absorption edge of SnO₂ and the A_1g Raman mode at 630 cm⁻¹ of the SnO₂ phonon spectrum were used to assess the presence of SnO₂ nanoclusters; the yield of X-ray induced paramagnetic E′ Sn centres was monitored to probe the variation in the amount of substitutional Sn centres. The results indicate that the clustering of SnO₂ becomes effective for Sn concentrations ≥ 0.8 mol% and it is competitive with the substitutional doping in xerogels densified at T ≥ 900 °C. No evidence of pre-existent clustering was observed in xerogels densified at lower temperatures in the investigated doping range.