Calorimetric characterization of photoinduced relaxation in GeSe ₉ glass

Enthalpy relaxation is measured during sub-band-gap irradiation of a GeSe ₉ sample. The glass undergoes rapid photorelaxation and reaches a saturated state that appears to correspond to a dynamic equilibrium between photoexcitation and thermodynamically driven relaxation. The activation energy for structural relaxation is measured and found to be small enough that the glass can fully relax in a few years at room temperature. A comparison of isochronal optical and thermal treatments shows that photorelaxation is not induced by laser heating but is rather due to an optically induced softening of the glass network. The photorelaxation process is interpreted as optically lifting the kinetic impediment to relaxation at room temperature. The kinetics of optically and thermally activated relaxation both show a nonexponential response, which can be fitted with a Kohlrausch function. It is shown that the relaxation kinetics increase with higher irradiation intensity.