Well-aligned ZnO nanorod arrays on Si substrate were synthesized based on a solution method. The scanning electron microscope, X-ray diffraction pattern and Raman spectrum show that the nanorods are vertically aligned to Si substrate following a c-axis one-dimensional growth direction. The photoluminescence (PL) spectra exhibit a strong ultraviolet emission and a broad weak green emission. The high-resolution transmission electron microscope, energy dispersive X-ray spectroscopy and PL spectra reveal that ZnO nanorods are high crystalline with the low density of defects. The origin of the green emission was investigated through varying post-treated conditions and it can be attributed to the oxygen vacancies (V-O). The growth mechanism was also discussed. (c) 2006 Elsevier B.V. All rights reserved.