Conformational disorder in vitreous systems probed by photoluminescence activity in SiO2

The emission bands alpha(E) (4.2 eV) and beta (3.1 eV) have been investigat ed in a variety of as-grown natural silica types. We report experimental re sults on the stationary photoluminescence spectra and their relationship wi th the absorption band B-2 beta (5.15 eV), on the temperature dependence of their competition, on their excitation pathway and their kinetic decay ens uing a pulse excitation. We use our results to characterize the electronic transitions involved and the intersystem crossing process linking the two e xcited states. Our results evidence the role played by the conformational d isorder. In particular, we make use of a model in which the interconversion processes between conformational substates are effective at high temperatu re (T > 200 K) and become frozen at low temperature (T < 120 K). Finally we discuss our results on the basis of a structural model ascribing these opt ical activities to an oxygen deficient center related to a Ge impurity. [S0 163-1829(99)03540-7].