Influence of ZnS and MgO Shell on the Photoluminescence Properties of ZnO Core/Shell Nanowires

By sequential growth of the core and shell of different materials, ZnO/ZnS and ZnO/MgO core/shell nanowire arrays are fabricated. Photoluminescence properties of these samples with different shell thicknesses are studied in detail. The results indicate that the ZnS shell thickness as a function of treatment time will noticeably change the photoluminescence intensity of the ZnO nanowires, whereas the MgO shell will not change the photoluminescence intensity any more after it saturates the surface dangling bonds of ZnO core. Large-scale first-principles calculations indicate that, unlike the ZnO/MgO core/shell nanowires, the electrons and holes of which are both confined in the core of the nanowires (type-I heterostructures), the ZnO/ZnS core/shell nanowires are type-II heterostructures, the electrons and holes of which are respectively confined in the core and the shell; as a result, the separation of electrons and holes in the ZnO/ZnS core/shell nanowires will reduce the spatial overlap between them, leading to the decrease of the photoluminescence intensity in this system. The experimental observations are in good agreement with first-principles calculations