Microstructure, crystallographic and photoluminescence examination of Ni doped ZnO nanoparticles co-doped with Co by sol–gel method

Zn0.96−xNi0.04CoxO nanoparticles with different Co concentration from 0 to 6% have been synthesized using sol–gel method. Phase purity of the synthesized samples was confirmed by X-ray diffraction (XRD) and energy dispersive X-ray (EDX) spectroscopy studies. The decreased crystallite size and the increased micro-strain by Co substitution confirmed the substitution of Co2+ instead of Zn2+ ions. Higher optical transmittance and optimal value of energy gap (3.44 eV) found in Zn0.92Ni0.04Co0.04O suggested that it can be taken as possible candidates for the industrial applications especially as transparent electrode. The defects related bluish-green absorption between 483 and 495 nm were due to the existence of oxygen vacancies and intrinsic defects. The strong blue and green band emission was noticed at higher Co-doping concentration due to the generation of new distortion centers in the lattice and surface defects which increases the intensity of green band emission.