Toward understanding the photoinduced changes in chalcogenide glasses

The various irreversible and reversible photoinduced phenomena in chalcogenide glasses, among them isotropic and anisotropic effects, were considered until now to have different origins. Upon reexamination, we find that the elemental photostructural steps are the same for all these phenomena. These are nonradiative recombinations via transient excitons yielding changes in local bonding configurations. The anisotropic changes arise from geminate recombinations of electron-hole pairs, which fail to diffuse out of the microvolume in which they were excited. A unified explanation of the large variety of photoinduced changes is presented.