Structure, X-ray photoelectron spectroscopy and photoluminescence investigations of the spray deposited cobalt doped ZnO thin films

A simple and cost-effective pneumatic spray pyrolysis technique (SPT) was employed to synthesize cobalt-doped zinc oxide (Co-ZnO) thin films onto the glass substrates at 450 °C. The effects of Co doping on the structural, optical, compositional, morphological and photoluminescence properties of ZnO thin films were investigated. XRD analysis confirmed the polycrystalline nature of the films having hexagonal crystal structure as well as successful incorporation of Co2+ ions into the lattice position of Zn2+ ions in the ZnO host. The traces of Co incorporation were confirmed by the shift of peak position of (0 0 2) plane, change in lattice parameters, the shift of optical absorption edge towards higher wavelength and observations of three bands related to d–d transitions. The observed band gap energy of Co-ZnO films decreases from 3.22 to 2.76 eV. The transmittance of the ZnO thin films decreases after Co doping. The X-ray photoemission spectra of doped films indicate the Co substitutes for Zn2+ and exist in +2 state. All the deposited pure and Co-ZnO thin films exhibit room temperature photoluminescence (PL).