Photoluminescence properties of surface-modified nanocrystalline ZnS : Mn

DBS surface-modified nanocrystalline ZnS:Mn was prepared by a precipitation method. Photoluminescence spectra and decay curves were measured and compa red to those of unmodified samples. For both kinds of samples, luminescence decay curves of 600 nm emission consist of two components with nanosecond (ns) and millisecond (ms) lifetimes. The nanosecond component is attributed to zinc vacancies luminescence, with peak located at 440 nm. While the mil lisecond component is attributed to Mn2+ luminescence and its decay time ch anges with Mn2+ concentration and surface modification. The surface-modifie d sample has a longer lifetime compared to unmodified samples. The photoagi ng of surface-modified samples is slow. Particle size effects on photoaging were also examined. For nanocrystalline ZnS:Mn photoaging is more noticeab le than that of bulk material. After UV irradiation, photoluminescence inte nsity of the modified sample is several times larger than that of the unmod ified sample, because the surface-active reagent decreases surface defects and depresses radiationless transitions. XPS yields direct evidence of the surface-modification effect on the surface structure. (C) 2000 Academic Pre ss.