Irradiation time dependence of Mn-doped ZnS nanocrystals with carboxylic acid on radiative and non-radiative transitions

ZnS nanocrystals doped with Mn2+ ions (ZnS:Mn) have attracted much attention in the past few years due to the changes in their optical properties in accordance with quantum confinement effects. ZnS:Mn nanocrystal systems form a new class of luminescent materials with some kind of applications because of the high fluorescence quantum efficiency. The addition of surface passivators and ultraviolet (UV) irradiation caused an increase of photoluminescence (PL) signal intensity. In this article, we report the UV irradiation time dependence of the optical absorption and PL signal intensities of ZnS:Mn nanocrystals with and without acrylic acid (AA). It is noted that the PL signal intensities of ZnS:Mn nanocrystals with and without AA undergo significant increases. On the contrary, the optical absorption intensities and/or non-radiative transition of ZnS:Mn nanocrystals with and without AA measured by photoacoustic (PA) technique decrease with the increase of UV irradiation. These experimental results suggest that there are possibilities of UV curing of the passivating AA polymer and photochemical reactions around the nanocrystals, which increase the fluorescence quantum efficiency