Theory of photostructural changes in glasses with negative-U centers: dependencies of steady-state photodarkening on gap-light intensity and frequency, pressure and temperature

Abstract

A theory is presented of a mechanism for the photostructural changes observed in semiconducting glasses. The theory takes into account that in these materials negative-U centers are the basic charge carriers, and gap-light generated excited states of such centers are accompanied by metastable “defects” in the original structure, which can be identified as the photostructural changes. The theory gives rise to a consistent interpretation, and some predictions, of dependencies of the steady-state photodarkening on gap-light intensity and frequency, pressure and temperature.