In this study, we report the diffusion mechanism of Er in GaN and the optical properties of Er-diffused GaN. The diffusion coefficient has been measured by Rutherford backscattering spectroscopy and secondary ion mass spectrometry. Erbium is also implanted into GaN to compare the photoluminescence (PL) characteristics. The PL emission of Er-diffused and implanted GaN can be observed in infrared region. The emission intensity efficiency related to the Er concentration distribution after the Er diffusion is discussed. (C) 2002 Elsevier Science Ltd. All rights reserved.