Improved Photoluminescence of MnS/ZnS Core/Shell Nanocrystals by Controlling Diffusion of Mn Ions into the ZnS Shell

Abstract

We studied the diffusion of Mn ions in MnS/ZnS core/shell nanocrystals (NCs) from the MnS core to the ZnS shell by steady-state and time-resolved photoluminescence (PL) spectroscopy. The colloidal MnS/ZnS core/shell NCs with different thicknesses of the ZnS shell synthesized in octadecene with nucleation doping strategy were annealed at different temperatures. It was found that the PL intensity and lifetime of the MnS/ZnS NCs with a thin ZnS shell significantly decreased with increasing annealing time in the heat treatment temperature range of 220−300 °C, resulting from the diffusion of Mn ions in the MnS/ZnS core/shell NCs to the surface of the ZnS shell, while the PL intensity and lifetime of the NCs with a thick ZnS shell remained almost constant in the temperature range. Furthermore, it was noted that the MnS/ZnS NCs with a small MnS core of about 2.0 nm in diameter exhibited high PL quantum yield of greater than 40%. The experimental results indicated that highly efficient luminescent Mn-doped ZnS NCs could be obtained by controlling the diffusion of Mn ions into the ZnS shell via annealing the core/shell NCs and using small-sized MnS cores and by optimizing the thickness of the ZnS passivating layer.