Effect of Ni doping on electrical, photoluminescence and magnetic behavior of Cu doped ZnO nanoparticles

Cu, Ni co-doped ZnO nanoparticles with different Ni concentrations between 0% and 4% were successfully synthesized by a simple co-precipitation method. Hexagonal wurtzite structure and phase purity of Zn0.96−xCu0.04NixO nanoparticles were confirmed by X-ray diffraction pattern. Higher dielectric constant, dielectric loss and electrical conductivity observed in Zn0.94Cu0.04Ni0.02O than the other samples were discussed based on the charge carrier density induced by Ni-doping. The presence of more distortion centers and interstitials in Ni=4% doped sample led to increase the crystallite size and hence the lattice volume. The electrical conductivity was maximum at Ni=2% due to the higher charge carrier density which was decreased at Ni=4% due to the scattering of charge carriers by defect centers. A dominant UV emission corresponding to the recombination of excited electrons from valence band with the holes in conduction band and defect related blue and green emissions were noticed in photoluminescence spectra. Room temperature ferromagnetism was observed in all the samples. The decrease of lattice distance between neighboring Cu-Cu ions and Ni-Ni ions by Ni doping enhanced the antiferromagnetic interaction and hence suppressed the room temperature ferromagnetism. The correlation between the structural and magnetic properties was discussed. The high coercivity at Ni=4% sample is explained in terms of high density of defects.