Zinc oxide (ZnO) films were prepared by thermal oxidation of metallic zinc films. The intensities of visible luminescence increase with oxidation time; however the shape and position of the green and yellow luminescence bands are determined by oxidation temperature only and do not vary with oxidation time and excitation laser powers. The green and yellow luminescent bands should originate from different intrinsic defects or defect complexes, which are formed in ZnO at certain temperatures. It suggests that the possibility of donor-acceptor pair recombination as the mechanism responsible for the green and yellow emissions can be excluded. (C) 2003 Elsevier Science B.V. All rights reserved.