Optical properties of ZnS:Mn2+ nanoparticles in polymer films

In this paper we report the abnormal phenomena observed in ZnS : Mn2+ nanoparticles embedded in polymer films. Irradiation-induced luminescence enhancement (IILE) effect was observed. The luminescence intensity of fresh samples under irradiation by 248 nm excimer laser light increases several folds with exposure time. After exposure, the luminescence intensity slightly decreases within hours, then reaches a stable value. Another abnormal property of ZnS:Mn2+ nanoparticles in PVB film is the thermal behavior of luminescence intensity. Luminescence intensity of Mn2+ nanoparticles in PVB film increases several times with temperature from 8 to 275 K, then decreases with temperature. A tentative model has been proposed, in which efficiency of energy transfer to Mn2+ ions increases with exposure. The electron states at the interface are expected to play an important role. The energy transfer to Mn2+ in ZnS nanoparticles is assumed to be phonon-assisted. The experimental data are fitted by the calculated curves. (C) 1998 Elsevier Science B.V. All rights reserved.