We have conducted a study of the material and infrared-luminescence properties of Er-implanted GaN thin films as a function of annealing. The GaN films, grown by metal-organic chemical-vapor deposition, were coimplanted with Er and O ions. After implantation, the films were furnace annealed at temperatures up to 1,100°C. Following each annealing stage, the samples were examined by photoluminescence (PL) measurements and secondary ion-mass spectrometry (SIMS) analysis. In the as-implanted samples, no PL signal near 1,540 nm could be detected with either above-bandgap or below-bandgap excitation. Only after annealing at temperatures above 900°C was the 1,540-nm luminescence detectable. Annealing at higher temperatures resulted first in an increase and then a decrease in the PL-signal intensities. The SIMS data showed that large concentrations of Al, O, and C atoms entered into the GaN films with high-temperature annealing. The stoichiometric changes in the GaN appear responsible for the changes in the Er-related luminescence.