Measurements were made of the temperature dependence, between 10 and 295K, of the lifetimes of the ultraviolet emissions associated with twofold coordinated Si and Ge, in pure and Ge-doped silica under excitation by synchrotron radiation. The Si-related fluorescence, centered at 4.4eV, had a single exponential decay and its lifetime decreased from 4.0 to 3.5ns upon increasing the temperature. The luminescence at 4.2eV, associated with the Ge defect, decayed with a single exponential dependence below 150K and with a more complex dependence at higher temperatures; its lifetime decreasing from 7.8 to 3.4ns. These features give evidence of the effectiveness of the thermally activated intersystem crossing in the relaxation of the excited singlet states, which was larger in the Ge-related center.

Ultra-Violet Emission Lifetime in Si and Ge Oxygen-Deficient Centers in Silica. M.Cannas, S.Agnello, R.Boscaino, F.M.Gelardi, S.Grandi, P.C.Mustarelli: Journal of Non-Crystalline Solids, 2003, 322[1-3], 129-33