THE ORIGIN OF REVERSIBLE AND IRREVERSIBLE PHOTOSTRUCTURAL CHANGES IN CHALCOGENIDE GLASSES

A model is proposed that describes both reversible and irreversible photostructural changes in vitreous and amorphous chalcogenides as resulting from recombination-induced bond rearrangements that accumulate during exposure time to produce a more disordered structure. The final light-saturated state depends on temperature, pressure, and light intensity and is characterized by diminished medium-range order. Reversible effects such as reversible photodarkening occur when the initial state is the annealed state. Irreversible structural changes such as photopolymerization and photodensification begin from initial states that are defined by material preparation conditions and are substantially different from the annealed state. Compositional trends observed in reversible photodarkening are discussed.