Luminescent mechanism of bulk and nano ZnS:Mn²⁺ phosphors

ZnS nanophosphors, with or without different concentrations of Mn ²⁺ activator ions, were synthesized by using the chemical precipitation method. Micron sized ZnS:Mn²⁺ powder was obtained from Phosphor Technology in the United Kingdom. Structure, morphology and particle sizes of the samples were determined by using XRD, TEM and SEM. The average particle size was ~3 nm in diameter. The band gap of ZnS nanophosphors, estimated from the UV-Vis data, was 4.1 eV. Luminescent properties of the samples were determined by photoluminescence (PL) measurements. Two emission peaks at 450 nm and 590 nm were observed from the micron sized sample. The 590 nm peak was red-shifted by 10 nm in the case of ZnS:Mn²⁺ nanophosphors used in this study. In this work a luminescent mechanism for both bulk (micron sized) and nano sized ZnS:Mn²⁺ is proposed, and the red-shifting is explained using the configuration coordinate model for Mn ²⁺.