Spectroscopic properties and mutual conversion reactions of quasimolecular hydroxyl and non-bridging oxygen defects in vitreous silica

Changes in the phonon sideband and the first overtone of O-H stretching vibrations caused by a neutron irradiation of hydroxyl containing vitreous silica indicate a formation of the interstitial hydroxyl groups. X-ray irradiation destroys bound hydroxyl groups producing non-bridging oxygen and interstitial hydrogen atoms, which are stable at 80 K. At higher temperatures atomic hydrogen becomes mobile and restores the O-H groups. The activation energy for its diffusion is 0.07±O.OI eV. The 1.85 eV fluorescence and 2.0 eV excitation/absorption bands of the non-bridging oxygen atom are due to partially forbidden transitions between non-bonding 2p orbitals.