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

Abstract

Violet-blue photoluminescence (β-band emission) of twofold-coordinated tin (O–Sn0–O, >Sn0) atoms in silica (SiO2) glasses, synthesized via a sol–gel route, was observed with a large band tail to longer wavelength. The presence of >Sn0 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 SiO2 glasses fiber. In the initial state of the new fabrication process, stannic oxide (SnO2) nanocrystals were precipitated in SiO2 glasses and an adequate annealing of SnO2–SiO2 glass ceramics in H2 gas led to the decomposition of SnO2 nanocrystals and concurrently the production of >Sn0 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 >Sn0 center, we could clarify the photoluminescence properties, by means of time-resolved fluorescence spectroscopy, and the >Sn0→Sn-E' conversion.