Photodarkening in amorphousAs2S3and Se under hydrostatic pressure

Abstract

Shifts in the optical-absorption edges induced by band-gap illumination and annealing under pressure have been studied for ${\mathrm{As}}_2$ ${\mathrm{S}}_3$ and Se. Both materials, if annealed at 1 atm beforehand, undergo a decrease in the band-gap energy with illumination under pressure. This decrease is accompanied by a similar degree of densification as that induced by annealing. The ${\mathrm{As}}_2$ ${\mathrm{S}}_3$ specimen annealed under pressure at the glass-transition temperature exhibits reversible photodarkening, the magnitude of which increases with pressure. These observations are accounted for quantitatively as resulting from an enhancement of the intermolecular interactions.