Light-induced memory in TlInS2 incommensurate ferroelectric

A new band at around 495 nm was observed in the photoluminescence spectra of TIInS2 incommensurate ferroelectric at similar to 15 K after an above-band gap laser treatment of the samples. Steady-state and time-resolved characteristics of this band pointed to a formation of the localized state in the band gap of TIInS2. This light-induced state was stable with time and against elevating the temperature up to incommensurate-paraelectric phase transition point at similar to 215 K. Further elevating the temperature into paraelectric-phase erased the state and the newly observed emission was going away from the spectra at similar to 15 K. It was found that the light irradiation could form the new state in the weak ferroelectric phase of TIInS2 at temperatures below similar to 20 K, but it could not at similar to 50 K. All the data obtained were reproducible. The observed phenomenon is attributed to a kind of memory effect and is discussed in terms of defect ordering and successive phase transitions in this material. (C) 2000 Elsevier Science B.V. All rights reserved.