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 the se materials (increased cubic susceptibility chi((3))). Flexible intrinsic structural units (oppositely charged chalcogen pairs) are suggested to be t he origin of photoinduced anisotropy, and account for its reorientation rev ersibility. I suggest that inflexible, photo-created, charged cation trappi ng sites dominate the mechanism of photorefraction. An increase of photoind uced anisotropy in glasses doped with Pr3+ ions is reported and attributed to Pr3+-induced increase of polarizability of charged charged chalcogen pai rs, when Pr3+ ions adhere to the negatively charged component of these pair s. The Boson peak in the Raman spectra of glasses increases with Pr3+-dopin g confirming an increase of polarizability of intrinsic structural units in to which Pr3+ ions are incorporated. The Boson peak also increases after pr olonged irradiation of chalcogenide glasses with near-gap-light indicating a light-induced creation of bonds with increased polarizability (e.g. broke n bonds), which cause photorefraction. Fatigue of host and Pr3+-dopant phot oluminescence in chalcogenide glasses induced by prolonged irradiation with near-gap-light is discussed in correlation with accompanying photorefracti on. (C) 1999 Elsevier Science B.V. All rights reserved.