Efficient Er-related photo-, cathodo-, and electroluminescence at 1539 nm was detected from Er and O co-implantedn-type GaN on sapphire substrates. Several combinations of Er and O implants and postimplant annealing conditions were studied. The Er doses were in the range(0.01–5)×1015ions/cm2and O doses(0.1–1)×1016ions/cm2. GaN films implanted with2×1015Er2+/cm2at 350 keV and co-implanted with1016O+/cm2at 80 keV yielded the strongest photoluminescence intensity at 1539 nm. The annealing condition yielding the strongest Er-related photoluminescence intensity was a single anneal at 800 °C (45 min) or at 900 °C (30 min) in flowingNH3. The optimum O:Er ratio was found to be between 5:1 and 10:1. Co-implanting the GaN:Er films with F was also found to optically activate the Er, with slightly (20&percent;) less photoluminescence intensity at 1539 nm compared to equivalent GaN:Er,O films. The Er-related luminescence lifetime at 1539 nm was found to depend on the excitation mechanism. Luminescence lifetimes as long as 2.95±0.15 ms were measured at 77 K under direct excitation with an InGaAs laser diode at 983 nm. At room temperature the luminescence lifetimes were 2.35±0.12, 2.15±0.11, and 1.74±0.08 ms using below-band-gap excitation, above-band-gap excitation, and impact excitation (reverse biased light emitting diode), respectively. The cross sections for Er in GaN were estimated to be4.8×10−21cm2for direct optical excitation at 983 nm and4.8×10−16cm2for impact excitation. The cross-section values are believed to be within a factor of 2–4. ©1997 American Institute of Physics.