Abstract
We report atomistic mechanisms that directly correlate the time-dependent optical responses of bulk Ge23Sb7S70 chalcogenide glasses to their metastable structural defects created and subsequently annihilated following gamma irradiation. These defects are characterized by an irradiation-induced increase in the concentration of edge-shared GeS4/2 tetrahedra bonding units, which gradually decreases to a pre-irradiation level during recovery, thus illustrating the glass' metastable behavior. This time-dependent structural change gives rise to the evolution of the glass's mass density that correspondingly induces a change and subsequent relaxation of linear refractive index and bandgap energy. Concurrent with this evolution in linear optical properties, the glass' nonlinear response is found to be unaffected, likely due to a counter effect associated with the glass network's free electrons.