Structure and photoluminescence studies on ZnS:Mn nanoparticles

ZnS:Mn was produced in nanocrystalline form by a chemical method using polyvinylpyroledone as a chemical capping agent. Mn was stoichiometrically substituted for Zn in ZnS. The manganese (Mn) concentration was varied over its whole solid solution limit in ZnS, i.e., from 0 to 40%. In the high concentration regime this material formed may be thus written as nanocrystalline (Zn, Mn)S. The material formed is thus a wide gap diluted magnetic semiconductor. The characterized material was in powder form. X-ray diffraction was used to estimate the crystallite size and to confirm formation of the material in single phase. The average crystallite size obtained was about 2 nm. The material remained cubic over the whole Mn solid solution range. The room temperature photoluminescence (PL) when deconvoluted using a Gaussian fit showed two extra peaks in nanocrystalline ZnS:Mn when compared to pure nanocrystalline ZnS, which had only two peaks. Mn incorporation significantly enhanced the PL intensity in nanocrystalline ZnS:Mn (400–850 nm range) thereby suggesting Mn2+ induced PL. The red shift of the two new peaks with increase in Mn2+ concentration can be attributed to the change in band structure due to the formation of ZnS:Mn alloy. These extra peaks were due to (a) various Mn2+ transitions in the ZnS host, (b) related to S as the nearest neighbor of Mn2+ ion in the nanocrystallite (due to the high concentration of Mn2+), or (c) Mn–Mn interactions at high Mn concentrations. However, our prepared pure MnS samples did not show any photoluminescence at room temperature. So it is concluded that the observed PL is Mn2+ induced in the nanocrystalline ZnS host.