In this study, we investigated the effect of post-annealing treatment on the UV photoluminescence of ZnO nanorods deposited on (0 0 0 1) GaN by hydrothermal synthesis. The temperature dependence of the photoluminescence spectra of ZnO nanorods annealed in nitrogen and oxygen was also studied. The as-grown ZnO nanorods were annealed in nitrogen and oxygen at 800 degrees C in 30 min. Results showed that UV light emission was greatly enhanced by annealing the as-grown ZnO nanorods in nitrogen ambient. Meanwhile, strong visible light emission was observed from the ZnO nanorods annealed in oxygen ambient. The effect of the annealing ambient and the photoluminescence temperature dependence were discussed with the relations to the structural defects. The time-resolved photoluminescence measurement was also proceeded to characterize the optical quality of the annealed ZnO nanorods. The decay times were 74 and 84ps for oxygen and nitrogen annealed ZnO nanorods, respectively. Once again, these results confirmed that the nitrogen annealed ZnO nanorods had better optical quality with less nonradiative related defects. (c) 2005 Elsevier B.V. All rights reserved.