Lattice-dynamical aspects in photoexcited chalcogenide glasses

Lattice-dynamical aspects are coherently applied to the reversible photostructural change (PSC) effect and associated phenomena in chalcogenide glasses. Far-infrared, X-ray photoelectron and optical absorption measurements reveal that photo-induced distortions and quenching in lattice configurations are characterized by increased randomness, which can be reversed by thermal annealing for full recovery. A statistical analysis reveals clearly that PSCs such as photodarkening and photoexpansion are essentially equivalent to a thermally frozen-in effect. The PSCs can be directly traced to the strong electron-lattice coupling and localized bond strain of chalcogenide glasses. A lattice-dynamic energy diagram highlights the importance of the quadratic-term of atomic distortion (δ q ) 2 in relating PSC to the glass transition phenomenon. The photochemical and photodoping effects are then described, on the same basis, in terms of the lattice fluctuation and high fictive temperature.