β-Band Photoluminescence and Sn-E′ Center Generation from Twofold-Coordinated Sn Centers in SiO_2 Glasses Produced via Sol-Gel Method

摘要

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.