Structure dependent photoluminescence and magnetic properties of Co:ZnS nanostructures

Co:ZnS nanostructures have been synthesized via the solvothermal method by modifying the stoichiometry of Zn and S sources in the solvothermal process. The structure and morphology analysis demonstrates that the increase of the Zn/S molar ratio leads to changes in the morphology and structure, from Co:ZnS nanorods and hexagonal nanocrystals to core-shell Co:ZnS/ZnO nanocrystals. The photoluminescence spectrum for Co:ZnS/ZnO exhibits strong visible light emissions due to the presence of a large amount of structural defects, whereas the emissions for Co:ZnS nanorods almost disappear because of the high crystallinity. All the samples display obvious room-temperature ferromagnetism. The saturated magnetic moment of the samples strongly depends on the concentration of structural defects in the nanostructures and can be effectively enhanced by the introduction of abundant defects.