Effect of annealing on lattice strain and near-band-edge emission of ZnO nanorods

The effect of air and oxygen annealing on the structural and the optical properties of hydrothermally synthesized ZnO nanorods was investigated. After hydrothermal synthesis, the resulting ZnO nanorods were annealed in air and under an oxygen atmosphere at 370°C for 1 h. X-ray diffraction results revealed that the oxygen-annealed nanorods possessed high crystallinity with a hexagonal-wurtzite crystal structure in the (002) plane. Evaluation of strain showed a tensile lattice strain of 0.426% resulting from oxygen annealing. The photoluminescence measurements showed that the relative intensity ratio of the near-band-edge emission (NBE) to the green emission (INBE/IGE) increased from ~2.6 for the as-grown ZnO nanorods to ~68.7 when the nanorods were annealed under oxygen. After annealing, a red shift of ~30 and ~44 meV in the NBE was observed for the nanorods that were annealed in air and under oxygen, respectively. This shift is attributed to the interaction between the neutral acceptors and the adsorbed oxygen atoms.