Mg+ ions (60 keV) were implanted into GaN nanowires (NWs) with total fluxes of 5 x 10(12)-5 x 10(14) cm(-2) followed by thermal annealing at 700 degrees C in NZ ambient. Transmission electron microscopic images showed amorphous layer formation and defect accumulation in the higher dose Mg-implanted GaN NWs after annealing. Photoluminescence spectra (300 K) of the annealed Mg-implanted GaN NWs exhibited near-band-edge (NBE) emission, donor-acceptor pair (DAP) emission, and defect-related yellow luminescence. With increasing dose, the NBE and DAP emissions are red shifted. Similar phenomena were observed in samples implanted with At to produce similar amounts of lattice disorder. The NWs show a much higher sensitivity to defect accumulation than GaN thin films. (C) 2008 Elsevier Ltd. All rights reserved.