A novel method to synthesize nanocrystalline AlxGa1-xN (0 <= x <= 1) powders is presented in this work. AlGaN nanocrystallites with the wurtzite structure were produced by thermal decomposition of a gallium-aluminum complex compound at 1000 degrees C in a three-zone horizontal quartz tube reactor under high-purity ammonia atmosphere. The crystallites showed a hexagonal structure, high homogeneity, and a narrow particle-size distribution at around 50 nm. A continuous composition range from 0 to 1 mol fraction can be reached by this method, allowing high control on the gallium and aluminum composition by monitoring the stoichiometry of the reaction between the metal nitrates and carbohydrazide. Low-temperature photoluminescence and cathodoluminescence studies showed that some impurities, such as carbon and oxygen, are unintentionally present in the final product and affect the optical properties. Subsequent thermal treatments between 900 and 1100 degrees C under an ammonia atmosphere significantly improved the quality of these materials. (C) 2007 Elsevier B.V. All rights reserved.