Enhanced photoluminescence of Mn:ZnS/ZnS core-shell nanocrystals synthesized by hot injection approach

Abstract

Heavy metal ions free core-shell nanostructures with Mn2+ ion doped ZnS as seed over coated with various thicknesses of ZnS shell (Mn:ZnS/ZnS core-shell structure) were prepared via hot injection method in the presence of oleylamine media. The effect of Mn2+ ion doping and shell thicknesses on structural and optical properties of Mn:ZnS/ZnS core-shell have been systematically studied by X-ray diffraction (XRD), UV-Vis, photoluminescence and time resolved photoluminescence spectroscopies. From XRD results, the growth of wurtzite ZnS shell on zinc blende seeds was observed due to the presence of primary amines during the shell formation. The minimal red shift in the UV-Vis spectrum of Mn:ZnS seeds after introducing Zn precursor indicates that the growth of ZnS shell on Mn:ZnS seeds. After being passivated by protective ZnS shell on Mn:ZnS seeds, the Mn2+ emission at 585 nm was greatly enhanced with increasing zinc precursor via reducing non radiative transitions due to the Mn2+ ions on the surface of nanocrystals. The Mn2+ ion emission have long excited state lifetime in the range of ms for all samples. Good photoluminescence and longer excited state life time of Mn:ZnS/ZnS core/shell offers a great potential for various applications ranging from solid state lighting to bio-imaging.