LATTICE-DYNAMIC 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 (deltaq)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.