Studies on the effect of UV irradiation on Mn-doped ZnS nanoparticles

With the advent of the increased attraction in compound semiconductors, attention has been focused on the research involving nanocrystalline Mn2+ doped ZnS (ZnS : Mn). In this paper, nano-scaled ZnS : Mn (both unpassivated and pasivated samples) was synthesized and we report the photoacoustic (PA) as well as photoluminescence (PL) properties upon exposure to ultraviolet (UV) light. It was found that passivation with acrylic acid (AA) yielded higher photoluminescence intensity. UV exposure caused a decrease in the PA intensity observed owing to a decrease in the nonradiative processes during exposure. A corresponding increase in the radiative processes was verified with the increase in the PL intensity during UV exposure. These experimental results suggest the possibility of UV curing for the passivating AA monomer and photochemical reactions around the nanocrystals, indicating the increase of the fluorescence quantum efficiency. Luminescent time decay measurements for the sample without AA showed a lengthening in the time decay constant after UV exposure. On the other hand, for the sample with AA, no change in the time decay constants was observed. This further strengthens the theory that during UV exposure, different luminescent decay mechanisms exist for the unpassivated and passivated samples.