Conformational disorder in vitreous systems probed by photoluminescence activity in (formula presented)

Abstract

The emission bands (Formula presented) (4.2 eV) and β (3.1 eV) have been investigated in a variety of as-grown natural silica types. We report experimental results on the stationary photoluminescence spectra and their relationship with the absorption band (Formula presented) (5.15 eV), on the temperature dependence of their competition, on their excitation pathway and their kinetic decay ensuing a pulse excitation. We use our results to characterize the electronic transitions involved and the intersystem crossing process linking the two excited states. Our results evidence the role played by the conformational disorder. In particular, we make use of a model in which the interconversion processes between conformational substates are effective at high temperature (Formula presented) and become frozen at low temperature (Formula presented) Finally we discuss our results on the basis of a structural model ascribing these optical activities to an oxygen deficient center related to a Ge impurity. © 1999 The American Physical Society.