Structural and photostructural properties of chalcogenide glasses: recent results from magnetic resonance measurements

We review nuclear quadrupolar resonance (NQR) and high-field (up to 30 T) nuclear magnetic resonance (NMR) measurements of As-75 in crystalline and glassy samples of arsenic chalcogenides. The results, which yield asymmetries in the electric field gradient at the arsenic sites, provide detailed information on the local structural order and the photoinduced structural changes in these glasses and crystals - order that cannot easily be obtained from other techniques such as X-ray or neutron scattering. In crystalline and glassy As2Se3 and As2S3 these results disagree with those inferred from previous low field Zeeman-perturbed NQR studies, and they are inconsistent with the predictions of a common model (Raft Model) for the structure of glassy As2Se3 and other chalcogenide glasses. Results on optically irradiated and annealed, glassy As2S3 place severe restrictions on the possible changes in local and intermediate range order that can occur on photodarkening. The high-field, NMR technique should be useful for many other solids that contain one of the 20 elements whose nuclei have spin 3/2 and relatively large quadrupole moments. (C) 2003 Elsevier B.V. All rights reserved.