Nanocrystalline SnO2 particles and twofold-coordinated Sn defect centers in sol-gel-derived SnO2-SiO2 glasses

Semiconductive nanocrystals of stannic oxide (SnO2) were precipitated in silica (SiO2) glasses synthesized via a sol-gel route. Kayanuma's equation, which describes the quantum confinement of an electron-hole pair in a semiconductive particle, well explained the absorption-edge shift due to the SnO2 nanocrystals in the optical absorption spectra. The adequate anneal of the SnO2-SnO2 glass ceramics in H-2 gas led to the decomposition of the SnO2 nanocrystals and concurrently the production of twofold-coordinated tin atoms (Sn-2(0)) that provided a violet photoluminescence. The thermal behavior was studied with the x-ray diffraction measurement and photoluminescence and photoluminescence excitation spectroscopy.