Effect of thermal annealing on dual photoluminescence emission characteristics of chemically synthesized uncapped Mn2+ doped ZnS quantum dots

•Effect of annealing on dual emission from ZnS:Mn quantum dots has been reported.•Quenching (~90%) of Mn2+ related PL intensity is observed at 600 °C temperature.•Cubic ZnS has been converted to wurtzite ZnO at 600 °C annealing temperature.•Visible light driven degradation of MB dye has been demonstrated.

Dual photoluminescence (PL) emission characteristics of Mn2+ doped ZnS (ZnS:Mn) quantum dots (QDs) have drawn a lot of attention recently. However, here we report the effect of thermal annealing on the PL emission characteristics of uncapped ZnS:Mn QDs of average sizes ~2-3 nm, synthesized by simple chemical precipitation method by using de-ionized (DI) water at room temperature. As-synthesized samples show dual PL emissions, having one UV PL band centred at ~400 nm and the other in the visible region ~610 nm. But when the samples are isochronally annealed for 2 h at 100-600 °C temperature range in air, ~90% quenching of Mn2+ related visible PL emission intensity takes place at the annealing temperature of 600 °C. X-ray diffraction data show that the as-synthesized cubic ZnS has been converted to wurtzite ZnO at 600 °C annealing temperature. The nanostructural properties of the samples are also determined by transmission electron micrograph, electron probe micro-analyser and UV-vis spectrophotometry. The photocatalytic property of the annealed ZnS:Mn sample has been demonstrated and photo-degradation efficiency of the as-synthesized and 600 °C annealed ZnS:Mn sample has been found out to be ~35% and ~61%, respectively, for the degradation of methylene blue dye under visible light irradiation. The synthesized QDs may find significant applications in future optoelectronic devices.