Microstructure, optical and FTIR studies of Ni, Cu co-doped ZnO nanoparticles by co-precipitation method

Zn0.96-xCu0.04NixO (0 <= x <= 0.04) nanoparticles were synthesized by co-precipitation method. The X-ray diffraction pattern showed the crystalline nature of prepared nanoparticles with hexagonal wurtzite structure. The average crystal size is decreased from 27 to 22.7 nm when Ni concentration is increased from 0% to 2% due to the suppression of nucleation and subsequent growth of ZnO by Ni-doping. The increased crystal size from 22.7 to 25.8 nm (Delta D similar to 3.1 nm) by Ni-doping from 2% to 4% is due to the creation of distortion centers and Zn/Ni interstitials. The cell parameters and volume of the lattice showed solubility limit at 2% of Ni doping. The energy dispersive X-ray spectra confirmed the presence of Cu and Ni in Zn-O. The optical absorption spectra showed that the absorption was increased up to Ni = 2% due to the creation of carrier concentration by Ni-doping and decreased beyond 2% due to the presence of more defects and interstitials in the Zn-Ni-Cu-O lattice. The observed red shift of energy gap from 3.65 eV (Ni = 0%) to 3.59 eV (Ni = 2%, Delta E-g approximate to 0.06 eV) is explained by sp-d exchange interactions between the band electrons and the localized d-electrons of the Ni2+ ions. The blue shift of energy gap from 3.59 eV (Ni = 2%) to 3.67 eV (Ni = 4%, Delta E-g approximate to 0.08 eV) is explained by Burstein-Moss effect. Presence of chemical bonding was confirmed by FTIR spectra. (C) 2014 Elsevier B.V. All rights reserved.