ZnO (O face) single crystals were implanted with 150 keV Er + ions to fluences of 5x10 1 4 and 5x10 1 5 Er + /cm 2 at room temperature. For fluences of 5x10 1 5 Er + /cm 2 the implantation damage raises the minimum yield from 2% to 22%. Despite the large amount of damage a fraction of 90% of the implanted Er ions are incorporated in substitutional sites along the [0001] axis. Photoluminescence (PL) studies reveal the presence of a weak emission near 1.54 μm at 77 K due to the 4 I 1 3 / 2 -> 4 I 1 5 / 2 transition of the Er 3 + ions. Annealing in oxidizing atmosphere at 800 o C leads to a reduction of the implantation damage, which is fully recovered after annealing at 1050 o C for 30 min. The annealing at 1050 o C leads to the outdiffusion of Er, with a 50% loss from the implanted region after the annealing. Only a fraction of 25% of the remaining Er is still in regular sites after the annealing and the Er 3 + PL vanishes.