Short-lived excited states of oxygen-deficient centers in amorphous SiO2

Samples of two pure silica glasses have been investigated by high--power pulsed cathodoluminescence as well as by synchrotron--photoluminescence and photoluminescence excitation spectroscopy with respect to the association of excitation and absorption bands to respective emission bands and the lifetime of excited defect states. The several types of structurally non--equivalent centers of the oxygen--deficient center (ODC) type were detected. The germanium related oxygen--deficient center shows luminescent bands at 3*1 and 4*3eV. It is shown that both the radiative transitions of the GeODC center are really interconnected by excitation and lifetime. The presence of the silicon related SiODC with a luminescent band at 4*5eV is established on the basis of characteristic decay time. The different schemes of radiative and non--radiative transitions for excited Ge-- and Si--related ODCs are discussed. The conclusion is made that the model of twofold coordinated Si and Ge atoms in silica glasses does not provide an adequate description of the fast relaxation of ODCs. Possible conversion mechanisms of short--living excited ODC--states are considered using an anomalous relaxation model for a neutral diamagnetic oxygen vacancy.