Photoluminescence behavior of SiO2 prepared by sol–gel processing

Two kinds of SiO2 were prepared by the usual sol–gel process (heat-treated sample) or a sol–gel process using photoirradiation (photoirradiated sample) and their photoluminescence behaviors were investigated. All heat-treated samples had photoluminescence bands, but none of the photoirradiated samples did. Intensity of emission of heat-treated sample increased as the treatment temperature increased. This photoluminescence behavior occurred reversibly with thermal treatment and photoirradiation. The network structure of SiO2 samples were evaluated by solid state NMR. The intensity of 17O solid state NMR peak increased with increased emission intensity. These results implied that heat-treated samples included some defects which showed photosensitivity, but the photoirradiated samples lacked such defects and formed a rigid network structure instead. These defects caused the observed photoluminescence.