PHOTOINDUCED ANISOTROPY IN PR-DOPED SULFIDE GLASSES WITH VARYING COMPOSITION AND PR CONTENT

Metastable photoinduced anisotropy (PA) generated by linearly polarize d sub-bandgap light is reported for undoped and Pr-doped Ge-S-I, Ge-Ga -S and As-Ga-S glasses with varying composition and Pr content. Compos itional trends of PA are related to the light-stimulated reorientation of intrinsic anisotropic centers and their environments, which vary w ith composition. These centers can be modeled with pairs of over- and under-coordinated sulfur atoms: the valence alternation pairs (VAPs). The addition of Pr up to a level of about 1000 ppm affects PA, suggest ing that this concentration is comparable with the concentration of VA Ps. Microscopic models are proposed for the centers responsible for PA in these glasses. (C) 1998 Elsevier Science B.V. All rights reserved.