Improvement of optical properties of post-annealed ZnO nanorods

Well aligned zinc oxide (ZnO) nanorods were synthesized on a Si substrate with a hydrothermal method. The effects of annealing on the optical properties of ZnO nanorods were examined by annealing samples in oxygen or forming gas (H2:N2=1:9). The optical properties of the ZnO nanorods were investigated using room temperature photoluminescence (PL) measurement, which revealed two emission bands. After each annealing, the intensity of ultraviolet (UV) emission increased, while the intensity of visible emission decreased. The reason for the increase in the ratio of UV to visible emission, IUV/IDLE, of ZnO nanorods annealed in oxygen or forming gas is attributed to the reduction in the concentration of the oxygen defects and to the less OH groups on the ZnO nanorod surface. Effects of crystal size, diameter, and chemisorbed oxygen were precluded.