β-Band Photoluminescence and Sn-E' Center Generation from Twofold-Coordinated Sn Centers in SiO₂ Glasses Produced via Sol–Gel Method

Violet-blue photoluminescence (β-band emission) of twofold-coordinated tin (O–Sn 0 –O, >Sn 0 ) atoms in silica (SiO 2 ) glasses, synthesized via a sol–gel route, was observed with a large band tail to longer wavelength. The presence of >Sn 0 centers more easily enabled us to produce Sn-associated E'-centers with X-ray irradiation, which is expected for a photosensitivity similar to that in the case of Ge-doped SiO 2 glasses fiber. In the initial state of the new fabrication process, stannic oxide (SnO 2 ) nanocrystals were precipitated in SiO 2 glasses and an adequate annealing of SnO 2 –SiO 2 glass ceramics in H 2 gas led to the decomposition of SnO 2 nanocrystals and concurrently the production of >Sn 0 point defects. Although the quantum efficiencies of the photoluminescence were very low to be 0.95% (external) and 1.3% (internal) under near-ultraviolet excitation owing to the triplet nature of the emissive level of >Sn 0 center, we could clarify the photoluminescence properties, by means of time-resolved fluorescence spectroscopy, and the >Sn 0 →Sn-E' conversion.