c-Axis oriented GaN nanocrystalline thin films were fabricated by nitridation of three different thin films of alpha-GaO(OH), alpha-Ga2O3 or beta-Ga2O3 obtained by sol-gel technique on amorphous quartz glass substrates. All these GaN thin films showed near band edge emission at 390 nm and yellow luminescence at 570 nm. The crystalline nature and c-axis orientation as well as luminescence properties of the GaN thin films increased by several times by using a buffer layer of GaN on the substrate. (C) 2008 Elsevier B.V. All rights reserved.