Eu-doped GaN with various ELL concentrations were grown by gas source molecular beam epitaxy, and their structural and optical properties were investigated. With increasing Eu concentration from 0.1 to 2.2 at%, deterioration of the structural quality was observed by reflection high-energy electron diffraction, atomic force microscopy and X-ray diffraction. Such a deterioration may be caused by an enhancement of island growth and formation of dislocations. On the other hand, room temperature photoluminescence spectra showed red emission at 622 nm due to an, intra-atomic f-f transition of Eu3+ ion and Fourier transform infrared spectra indicated an absorption peak at about 0.37eV, which may be due to a deep defect level. The intensity of the red luminescence and the defect-related absorption peak increased with increasing Eu concentration. and a close correlation in the increasing behavior was observed between them. These results suggest that the deep defect level plays an important role in the radiative transition of ELL 3, ion in GaN and the optical process for the luminescence at 622 nm was discussed with relation to the defect. (C)2002 Elsevier Science B.V. All rights reserved.