The Photoexpansion in Chalcogenide Glasses: Excitonic Effects in S/Se Chains and Rings

It is known that chalcogenide glasses such as Se and As 2 S 3 exhibit transitory volume expansion under light excitation. We consider its mechanism through numerical analyses, the result being interpreted using simple ideas. Ab initio molecular‐orbital calculations reveal that one‐dimensional H– n S(Se)–H chains ( n = 2–14) and crown‐shaped S/Se rings, when excited, undergo marked atomic changes; bond‐distance lengthening and angular widening, which could work as essential origins of the macroscopic photoexpansion. We grasp these changes, taking Mulliken‐charge variations under excitation into account, as exciton self‐trapping (polaronic) effects in molecular wires. The photoexpansion may be universal to one(or low)‐dimensional systems.