Authors: M.M. Biggs, O.M. Ntwaeaborwa, H.C. Swart, M.J.H. Hoffman
Affilation: University of the Free State, South Africa
Pages: 543 - 546
Keywords: luminescent mechanism, nano phosphors, ZnS:Mn2+
In this study ZnS nanophosphors, with or without different concentrations of Mn2+ activator ions, were synthesized by using the chemical precipitation method. Luminescent properties of the samples were determined by photoluminescence (PL) measurements. Two peaks at 450 nm and 590 nm are observed for the bulk sample, while the second peak showed a red shift of 10 nm in the case of the nano sample. A proposed luminescent mechanism for both bulk and nano ZnS:Mn2+ is given. A blue shift in the excitation and absorption spectra of nano ZnS:Mn2+ is observed. This blue shift is explained according to the energy dispersion diagram for bulk and nano semiconductors. The PL peak that was observed at 450 nm can be attributed to hole and electron trapping by defect states (zinc or sulphur vacancies) and subsequent recombination of these electrons and holes. The peak at 590 nm for the bulk sample and the one at 600 nm for the nano sample can be attributed to the 4T1 - 6A1 transition of Mn2+. This red shift in the peak can be explained according to the configuration coordinate model for Mn2+. Clarification of this mechanism will help us with the custom design of these phosphors.