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

Abstract

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 22.7nm 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 25.8nm (ΔD∼3.1nm) 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 3.65eV (Ni=0%) to 3.59eV (Ni=2%, ΔEg≈0.06eV) 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 3.59eV (Ni=2%) to 3.67eV (Ni=4%, ΔEg≈0.08eV) is explained by Burstein–Moss effect. Presence of chemical bonding was confirmed by FTIR spectra.