Solvothermal synthesis and photoluminescence properties of ZnS:Mn2+/ZnO core-shell nanocrystals

High-quality ZnS:Mn2+ and ZnS:Mn2+/ZnO core-shell nanocrystals (NCs) were synthesized via a solvothermal method, and characterized by X-ray diffraction (XRD), Transmission electron microscopy (TEM), ultraviolet-visible (UV-vis) and photoluminescence (PL) spectra. Compared with the bare ZnS:Mn2+ NCs (10 nm), the obtained ZnS:Mn2+/ZnO core-shell NCs have a smaller size (4 nm) and better dispersion, which could be attributed to the added ammonia that adsorbed on the surface of ZnS nuclei and hindered their further growth. From the PL spectrum of ZnS:Mn2+NCs, orange luminescence at about 595 nm is observed, which is attributed to the 4T1-6A1 transition of the Mn2+. Meanwhile, the PL intensity of the ZnS:Mn2+/ZnO core-shell NCs is enhanced, and the emission peak is shifted from 595 to 581 nm. The enhancement of the PL intensity is due to the elimination of the surface defects after the growth of the ZnO shell on ZnS:Mn2+ NCs, while the peak blue shift is mainly ascribed to the stress from the mismatch of lattice constants between ZnS and ZnO NCs.