GaN particles of different sizes were separated by a sedimentation technique. We find that a correlation exists between the cathodoluminescence (CL) spectra of the particles and their average sizes. These results imply that the particles contain a substantial fraction of GaN nanocrystallites (NCs) whose emission is shifted by quantum size effects and whose proportions differ with the overall size of the particle. X-ray photoelectron spectroscopy data combined with ion etching show that the NCs comprising these clusters have a GaN core surrounded by a gallium oxide shell. The results indicate that size-separated GaN particles may be useful CL sources of light for exciting phosphors over a range of UV wavelengths without the need for alloys such as AlGaInN. (C) 2004 American Vacuum Society.