We obtained well-aligned ZnO nanowire arrays by chemical vapor deposition. The XRD patterns show that the crystallinity is improved by O-2 annealing at 800 degrees C. The field emission (FE) properties of annealed ZnO nanowire arrays become worse. The photoluminescence spectra show that the decrease of oxygen vacancy densities in ZnO nanowire arrays is responsible for the degraded FE properties. (C) 2015 Elsevier B.V. All rights reserved.