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 ð0:0 x 0:1Þ, 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 þ 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 (VO) concentration by increasing the Ni doping. The saturation
magnetization and coercivity also increase with Ni doping, indicating a strong correlation between the
concentration of VO 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 sped exchange interaction, which is
mediated by the VO defects in the ZnO lattice.