Abstract

Ge-rich ternary chalcogenide glasses (ChGs) exhibit photobleaching (PB) when illuminated with bandgap light. This effect originates from the combined effects of intrinsic structural changes and photo-oxidation. In a sharp contradiction to previous observations, in this Letter, we demonstrate, for the first time, that Ge-rich ${\mathrm{Ge}}_{25}{\mathrm{As}}_{10}{\mathrm{Se}}_{65}$ ChG thin films exhibit photodarkening (PD) at 20 K and PB at 300 and 420 K after having been continuously illuminated for $\sim 3$ hours. The temporal evolution of PD/PB shows distinct characteristics at the temperature of illumination, and provides valuable information on the light-induced structural changes. Furthermore, structure-specific far-infrared (FIR) absorption measurements give direct evidence of different structural units involved in PD/PB at the contrasting temperatures. By comparing the light-induced effects in vacuum and air, we conclude that intrinsic structural changes dominate over photo-oxidation in the observed PB in ${\mathrm{Ge}}_{25}{\mathrm{As}}_{10}{\mathrm{Se}}_{65}$ ChG thin films.

© 2015 Optical Society of America

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