Photorefractivity in nanostructured tin-silicate glass ceramics: a radiation-induced nanocluster size effect

The possibility of obtaining permanent photoinduced refractive index changes, up to $\ensuremath{-}{10}^{\ensuremath{-}3}$, in nanostructured silica-based composites has been demonstrated in ${\mathrm{S}\mathrm{i}\mathrm{O}}_{2}\ensuremath{\mathbin:}{\mathrm{S}\mathrm{n}\mathrm{O}}_{2}$ optical-grade glass ceramics exposed to ultraviolet radiation. Optical and electron paramagnetic resonance data suggest that the negative refractive index change involves a modification at the surface of the ${\mathrm{S}\mathrm{n}\mathrm{O}}_{2}$ nanoclusters, leading to a reduction of their crystalline size.