Wurtzite GaN and (Ga,Zn)N nanocrystals with the size of 8-20 nm were synthesized by the solid-phase thermal decomposition method at mild temperature of 350-650 degrees C. This synthesis method is a simple and low cost method. From the further study on the luminescence mechanism, Zn dopant introduces new energy levels in the band gap of GaN nanocrystals, which effectively induces the fluorescence emission in the visible region. In addition, the VN-H defect significantly affects the optical properties of nanocrystals. Moreover, GaN nanocrystals with a proper Zn-doping concentration will produce a white light. (C) 2013 Elsevier B. V. All rights reserved.