Polar and non-polar ZnO films were synthesized on different planecuts (a-, c- and R-planes) of Al2O3 substrates by metal-organic vapor-phase epitaxy. Polar ZnO films were obtained on c- and a-Al2O3 substrates whereas non-polar ZnO films were obtained on R-Al2O3 substrates. In spite of generally better crystalline quality and optical properties of polar ZnO films, there are two characteristic photoluminescence peaks detected in the non-polar material only. The peaks (at 3.048 and 2.966 eV) are tentatively assigned to electron transitions involving zinc vacancy and oxygen interstitial defect states, respectively. (C) 2008 Elsevier B.V. All rights reserved.