ZnO films were deposited by metal-organic chemical vapor deposition on (0001) sapphire substrates at various partial pressure ratios of oxygen and zinc precursors (R(VI/II)). The annealing and the R(VI/II) ratio effects on the vibrational and optical properties of ZnO films have been investigated by Micro-Raman scattering and low temperature photoluminescence (PL) spectroscopy. As confirmed by characterizations used in this study, the quality of the ZnO films was improved by thermal annealing at 900 degrees C in oxygen ambient. Raman spectra of the as-deposited films show a broad band (BB) centered at about 518 cm(-1) whose intensity increases when the R(VI/II) ratio decreases. After annealing, the intensity ratio of the BB to the E(2) high (E(2)(H)) peak decreases rapidly with increasing the annealing time (t(an)). The vibrational properties of the annealed films grown at R(VI/II) = 1 need only 1 h to be improved in contrast to those of films grown in Zn-rich condition, which need 4 h. From the E(2)(H) mode frequency, the residual stress in both the as-grown and the annealed films has been estimated. Micro-Raman measurements show that as-grown films are under a compressive stress which vanishes upon annealing and is not strongly dependent on tan for tan up to 1 h. PL spectra show that sharp donor bound exciton and A-free exciton emissions are observed for the as-deposited films grown at R(VI/II) >= 0.5 and are enhanced after annealing for 1 h. However, in ZnO films grown in Zn-rich condition these emissions are absent and a t(an) = 4 h is needed to annihilate non-radiative recombination centers and improve their luminescent efficiency. (C) 2010 Elsevier BM. All rights reserved.