Gallium nitride-gallium oxide structures were formed by heat-treating gallium nitride (GaN) powders in several gas environments at temperatures from 400degreesC to 900degreesC. The platelet nanostructured particles were examined at several stages of oxidation by microscopic, structural, chemical and optical spectroscopic techniques. Particle morphology, nanophase characterization and photoluminescence data showed that the oxide layers passivate the GaN platelets surfaces and significantly reduce the yellow emission while enhancing near band-edge emission. (C) 2004 Elsevier Inc. All rights reserved.