Configurational and Structural Models for Photodarkening in Glassy Chalcogenides

Abstract

Mechanisms of the reversible photodarkening phenomenon have been studied for amorphous S and Se. These materials exhibit smaller photodarkening effects when illuminated with sub-bandgap illumination at 80 K. A configurational model is proposed for interpreting the results, and parameters characterizing the model are estimated. This model is connected with a structural model which assumes photoinduced bond twisting. By using the modified valence-forcefield constants, it is shown that the structural model is quantitatively consistent with the configurational model. These models can explain most experimental results related to photodarkening, including the pressure and temperature dependence. The models can also be applied to photodarkening in glassy chalcogenide alloys.