Photoinduced effects in undoped and rare-earth doped chalcogenide glasses: review

The mechanisms of metastable photoinduced anisotropy and photorefraction in chalcogenide glasses are proposed based on increased polarizability of these materials (increased cubic susceptibility chi((3))). Flexible intrinsic structural units (oppositely charged chalcogen pairs) are suggested to be the origin of photoinduced anisotropy, and account for its reorientation reversibility. I suggest that inflexible, photo-created, charged cation trapping sites dominate the mechanism of photorefraction. An increase of photoinduced anisotropy in glasses doped with Pr3+ ions is reported and attributed to Pr3+-induced increase of polarizability of charged charged chalcogen pairs, when Pr3+ ions adhere to the negatively charged component of these pairs. The Boson peak in the Raman spectra of glasses increases with Pr3+-doping confirming an increase of polarizability of intrinsic structural units into which Pr3+ ions are incorporated. The Boson peak also increases after prolonged irradiation of chalcogenide glasses with near-gap-light indicating a light-induced creation of bonds with increased polarizability (e.g. broken bonds), which cause photorefraction. Fatigue of host and Pr3+-dopant photoluminescence in chalcogenide glasses induced by prolonged irradiation with near-gap-light is discussed in correlation with accompanying photorefraction. (C) 1999 Elsevier Science B.V. All rights reserved.