Influence of nickel doping on the energy band gap, luminescence, and magnetic order of spray deposited nanostructured ZnO thin films

We synthesized Ni doped ZnO thin films, ZnxNi1-xO (0.0 <= x <= 0.1), using spray pyrolysis deposition and performed a systematic study on their crystal structure, electronic, photoluminescent properties, and magnetic order. X-ray diffraction analysis showed that all nanostructured films under investigation are crystalized in a single phase wurtzite structure (space group P63mc), with a preferred orientation along (002) plane. The phase purity and the successful incorporation of Ni dopants into the ZnO lattice were also confirmed by the x-ray photoelectron spectroscopy (XPS), Ultra Violet-Visible, and Energy Dispersive X-ray spectroscopy measurements. The XPS results indicated that Ni ions are in 2 + oxidization state in all doped films. Photoluminescence (PL) spectroscopy showed strong emission peak in the UV region and multi-components emission peak in the visible luminescence, which is ascribed to deep-level emissions by different types of intrinsic defect states. Both XPS and PL spectroscopy clearly showed significant enhancement in the oxygen vacancy (V-O) concentration by increasing the Ni doping. The saturation magnetization and coercivity also increase with Ni doping, indicating a strong correlation between the concentration of V-O defects, and the observed magnetic order in the doped films. In addition, a red shift in the energy gap is found with Ni doping and is attributed to the sp-d exchange interaction, which is mediated by the V-O defects in the ZnO lattice. (C) 2019 Elsevier B.V. All rights reserved.