We report on the low energy oxygen implantation induced improvement in crystallinity and optical properties of surface modified ZnO single crystals. Undoped ZnO (0 0 0 1) single crystal wafers are implanted with 100 keV oxygen ions at a dose of 5 x 10(13) and 5 x 10(14) cm (2) and subsequently annealed at 500 and 600 degrees C in oxygen ambient. The as-implanted and annealed ZnO wafers are studied by Rutherford back scattering spectrometry (RBS), channeling, Raman, photoluminescence (PL), and Fourier transform infrared spectroscopy (FTIR). Channeling studies show a relatively high chi(min) (> 20%) in the virgin ZnO wafer. After implantation and two-step annealing, RBS studies show improved crystallinity. Raman line width analysis for the E-2(high) mode indicates reduction in strain in the annealed samples as compared to the virgin ZnO wafer. As-implanted samples show drastic quenching of the near band-edge (NBE) PL band due to defects created by the implantation. However, after two-step annealing, the low-dose implanted sample show a five-fold increase in intensity ratio of NBE band (376 nm) to defect related broad band (similar to 530 nm) at room temperature. Implantation induced changes in the composition and improved crystallinity in the near surface region is accounted for the major improvement in the PL emission. (C) 2009 Elsevier B. V. All rights reserved.