Microstructures and luminescence behaviors of Mn super(2+) doped ZnS nanoparticle clusters with different core/shell assembled orders

Mn super(2+) doped ZnS nanoparticle (NP) clusters composed of densely packed ZnS:Mn super(2+) NPs, ZnS/ZnS:Mn super(2+) core/shell NPs, or ZnS:Mn super(2+)/ZnS core/shell NPs were prepared by a chemical co-precipitation method. Estimation of the lattice parameters and the band gap of the ZnS NP clusters through X-ray diffraction and optical diffuse reflectance spectra showed no noticeable divergence due to Mn super(2+) dopants. Transmission electron microscopy revealed that ZnS:Mn super(2+)/ZnS NP dusters contained much larger NP crystallites associated with the high growth rate of undoped ZnS shell layers. In contrast, Mn super(2+) dopants limited the deposition of ZnS:Mn super(2+) shell layers, leading to smaller particle sizes of ZnS:Mn super(2+) and ZnS/ZnS:Mn super(2+) NPs in the clusters. Among all the samples, ZnS/ZnS:Mn super(2+) NP clusters exhibited the most intense orange emission of Mn super(2+), which was further confirmed by the estimated energy transfer (from ZnS to Mn super(2+)) efficiency values, i.e., ZnS/ZnS:Mn super(2+) (42.1%) > ZnS:Mn super(2+)/ZnS (15.9%) > ZnS:Mn super(2+) (1%). An energy migration mechanism was proposed for interpreting the high energy transfer efficiency of the ZnS/ZnS:Mn super(2+) structure.