The structure and optical properties of ZnO nanocrystals dependence on Co-doping levels

Pure and Co-doped ZnO (Co:ZnO) nanocrystals with different doping levels were synthesized via a coprecipitation process. The structure and morphology of the as-prepared samples were characterized by XRD, EDS, XPS and FESEM. Results show that cobalt ions, in the oxidation state of Co2+, replace Zn2+ ions into the ZnO lattice without changing its wurtzite structure. The dopant content varies from 0.35 to 2.94% depending on Co-doping levels. The particles have a nearly spherical morphology with dimensions of 80–150 nm for pure ZnO and 50–120 nm for Co:ZnO. The optical properties of the samples were studied by UV–vis absorption and PL spectra. The band gap of Co:ZnO nanocrystals decreases with the increasing dopant content, resulting in red shifts of the wavelength in UV absorption and PL emissions.