We describe the first stage of the evolution of CL spectra, intensity and dislocation contrast under low keV electron beam for ELO-GaN with a low dislocation density. The UV and yellow intensities are decreased by beam irradiation. We have observed a broadening of the UV peak towards low energies followed by a red shift. This is explained in terms of an electron beam activation of non-radiative centers which relax partially the compressive strain, The dislocation contrast is lowered, but the dislocations become more non-radiative. We suggest that dislocations are preferential ways for the flux of non-radiative centers from the coalescence boundaries to the bulk. (C) 1999 Elsevier Science B.V. All rights reserved.