Morphological transformations in cobalt doped zinc oxide nanostructures: Effect of doping concentration

Effect of doping concentration on the morphological, vibrational and optical properties of ZnO nanostructures has been studied systematically. Incorporation of cobalt into the ZnO lattice is found to gradually transform the morphology from hexagonal cylinders to rods for nominal Co concentration of 1-10 at%, respectively. An increase in hydroxyl ion concentration in the Co precursor leads to a preferential growth along [001] direction, giving rise to the formation of rod-like structures for high Co concentrations. Based on the structural characterization, a model for morphological evolution of microstructures has been proposed. Debye-Scherrer analysis of XRD pattern reveals an increase of the crystallite size with doping concentration. The band gap, calculated using a Kubelka-Munk method, reveals a decrease in the absorption onset with an increase in the doping level. Raman analysis reveals the basic as well as impurity phases and FT-IR analysis confirms the incorporation of cobalt-doping. Photoluminescence analysis provided further insight of the optical processes altered with the Co doping.