Zinc oxide (ZnO) thin films were prepared on quartz substrate using radio frequency magnetron sputtering at various oxygen/argon (O-2/Ar) flow ratios. The structural and optical properties of ZnO films were investigated in dependence of O-2/Ar ratio and annealing temperature by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Raman scattering spectroscopy, UV-visible spectroscopy and photoluminescence (PL) spectroscopy. XPS spectra showed that the peak positions of the O1s and Zn 2p shifted to opposite directions of binding energy with increasing O-2/Ar flow ratio, and the as-deposited ZnO films changed from the Zn-rich to O-rich. Raman spectra revealed that ZnO films consisted of wurtzite structure exhibited high crystalline quality and c-axis preferred orientation after annealing at 420 degrees C. The transmittance and energy band gap (E-g) of the as-deposited ZnO films increased with increasing O-2/Ar flow ratio. As the films were annealed, the E-g decreased first and then increased with annealing temperature. The PL spectra indicated that all films exhibited a violet emission peak and the ZnO films prepared at O-2/Ar = 35/35 showed an additional green emission. The origin of both emission peaks and the change in the intensity with O-2/Ar ratio and annealing temperature were discussed. (C) 2012 Elsevier B.V. All rights reserved.