High-density ZnO nanorods were vertically grown on Si coated with ZnO film (ZnO/Si substrate) from aqueous solution at low temperatures. The ZnO nanorods after annealed in various atmospheres still present good c-axis crystalline character but exhibit remarkable differences in photoluminescence (PL) properties. Enhancement of PL properties due to N-2-atmosphere annealing for ultraviolet emission can be attributed to the reduction of defect density because the nonparamagnetic singly ionized state (N-) can easily occupy the oxygen vacancies as evidenced by Raman spectroscopy and electron paramagnetic resonance spectrometry. The extended x-ray absorption fine structure reveals that the annealing atmosphere shows no apparent influence on the deep-level defects of ZnO nanorods except that some ions are possibly trapped or adsorbed on the surface of the ZnO nanorods. (c) 2005 American Vacuum Society.