Role of lone-pair electrons in reversible photostructural changes in amorphous chalcogenides

Results of in-situ X-ray absorption fine structure and Raman scattering measurements of photostructural change in amorphous selenium and binary As,Se, glass are reported. It is demonstrated that in the photoexcited state the coordination number of selenium species increases reversibly. This increase is caused by the formation of dynamic interchain (interlayer) bonds via interaction of excited electrons of lone-pair orbitals whose presence is essential for the process to occur. After subsequent bond breaking a transition to a metastable state takes place. (C) 1998 Elsevier Science B.V. All rights reserved.