Single crystalline Eu- or Tb-doped GaN was grown with the rare earth content up to 2% by molecular beam epitaxy (MBE) using ammonia. Sharp luminescence peaks originating from intra-atomic f-f-transition of the rare earth were observed, however, the intensity of Eu-doped GaN is two orders of magnitude stronger than that of Tb. The cause of the remarkable difference in the luminescence intensity between Eu- and Tb-doped GaN was discussed based on the coordination symmetry around the rare earth elements. (C) 2002 Elsevier Science B.V. All rights reserved.