Triplet state in high-purity silica glasses

Electron spin resonance in the spectral region about g=4, believed to be due to a triplet state, is investigated in y-irradiated high-purity silica glasses. The signal in this spectral region was first reported by Griscom, who attributed it to a cavity-like triplet state formed by chlorines. The signal near g=4 in the present study is found only in oxygen deficient samples (samples with optical absorption at 5.0-eV and 7.6-eV prior to y-irradiation). One of these oxygen deficient samples contains no chlorine, but instead contains florine. The signal intensities of the triplet are in good agreement with the chlorine or florine contents. These results suggest that the signal is due to a biradical at an oxygen deficient site (≡Si• •Si≡). When the samples are heat-treated in hydrogen atmosphere prior to y-irradiation, the triplet signal disappears, but not when treated with hydrogen at room temperature. This is consistent with the behavior of the oxygen vacancy (judging from the 5.0-eV absorption intensity), which is terminated by hydrogen-treatment at elevated temperature but remains after hydrogen-treatment at room temperature.