Monocrystalline Ni-doped ZnO nanorods were synthesized through a chemical method. The average length and diameter of these nanorods were in the ranges of 400–700nm and 25–40nm, respectively. Structural analyses revealed that the Ni-doped ZnO nanorods were of pure wurtzite hexagonal phase and grew along the preferred c-axis direction. X-ray photo-electron spectroscopy gives evidence that the Ni dopant was in the +2 valence oxidation state and was uniformly distributed in the nanorods. Full multiple-scattering ab initio calculations of Ni K-edge X-ray absorption near edge structure analysis revealed that Ni impurity atoms were substitutionally incorporated into ZnO host without formation of secondary phases (Ni metal and Ni2O3). The comparison of experimental and simulated X-ray absorption near edge structure spectra on Ni K edge revealed the presence of the oxygen vacancy (native defect) in the prepared nanorods. Photoluminescence spectrum exhibited two emission peaks, which were ascribed to near band edge transitions and broadened intensive green emission associated with oxygen-vacancy defects. Furthermore, the magnetic measurements revealed that the nanorods exhibited intrinsic room-temperature ferromagnetism. Ferromagnetic ordering was interpreted by the overlapping of polarons mediated through oxygen vacancy based on the bound magnetic polaron model.

Oxygen-Vacancy-Induced Green Emission and Room-Temperature Ferromagnetism in Ni-Doped ZnO Nanorods. Iqbal, J., Wang, B., Liu, X., Yu, D., He, B., Yu, R.: New Journal of Physics, 2009, 11[6], 063009