Single crystals of sapphire (Al2O3) with (0001), (1010) and (1120) orientations were implanted at 623 K with 110 keV Ar ions to fluence of 9.5×1016 cm-2. The ion-implanted Al2O3 samples were annealed at 873, 1073, 1273 and 1373K for 60 min in vacuum and in air, respectively. Photoluminescence (PL) spectra of the as-implanted samples showed an emission band at 506 nm, with excitation wavelength at 300 nm. The PL peak intensity of (0001) and (1010) orientation samples were maximum after annealing at 1073K in both vacuum and in air. The annealing in air at 873, 1073 and 1273K lead to much higher PL peak intensity compared to annealing in vacuum. In all the samples the emission band disappeared after annealing at 1373K both in vacuum and in air. The experimental results indicate that annealing temperature, annealing atmosphere and crystal orientation play important roles for the PL peak intensity at 506nm of sapphire implanted with Ar ions. The PL peak at 506nm after Ar-implantation and annealing is related with the population of interstitial Al atoms introduced by the ion bombardment and the formation of argon gas bubbles and the resolution of Ar atoms during annealing.