Microstructures and luminescence behaviors of Mn2+ doped ZnS nanoparticle clusters with different core/shell assembled orders

Highlights: • ZnS:Mn2+@ZnS NPs were grown to be larger than ZnS:Mn2+ and ZnS@ZnS:Mn2+. • PL was mainly influenced by energy migration (EM) from core to shell layers of NPs. • ZnS and Mn2+ acted as activator and sensitizer of the EM processes, respectively. • S2− vacancies acted as migrators between ZnS in the core and Mn2+ in the shell. • An optimized EM route length was founded in ZnS@ZnS:Mn2+ NPs, so it got efficient PL. -- Abstract: Mn2+ doped ZnS nanoparticle (NP) clusters composed of densely packed ZnS:Mn2+ NPs, ZnS/ZnS:Mn2+ core/shell NPs, or ZnS:Mn2+/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 Mn2+ dopants. Transmission electron microscopy revealed that ZnS:Mn2+/ZnS NP clusters contained much larger NP crystallites associated with the high growth rate of undoped ZnS shell layers. In contrast, Mn2+ dopants limited the deposition of ZnS:Mn2+ shell layers, leading to smaller particle sizes of ZnS:Mn2+ and ZnS/ZnS:Mn2+ NPs in the clusters. Among all the samples, ZnS/ZnS:Mn2+ NP clusters exhibited the most intense orange emission of Mn2+, which was further confirmed by the estimated energy transfer (from ZnS to Mn2+) efficiency values, i.e., ZnS/ZnS:Mn2+ (42.1%) > ZnS:Mn2+/ZnS (15.9%) > ZnS:Mn2+ (1%). An energy migration mechanism was proposed for interpreting the high energy transfer efficiency of the ZnS/ZnS:Mn2+ structure