Structure and luminescence of nanocrystalline gallium nitride synthesized by a novel polymer pyrolysis route

Thermal decomposition in a horizontal quartz tube reactor of a polymer [-(CH6N4O)3Ga(NO3)3-] in a nitrogen atmosphere, yield directly nano-structured gallium nitride (GaN) powder. The polymer was obtained by the reaction between high purity gallium nitrate (Ga(NO3)3) dissolved in toluene and carbohydrazide as an azotic ligand. The powder synthesized by this method showed a yellow color and elemental analysis suggested that the color is due to some carbon and oxygen impurities in the as-synthesized powder. Electron microscopy showed that the as-synthesized powders consist of a mixture of various porous particles containing nanowires and nano-sized platelets. The size of the crystallites can be controlled by annealing processes under ammonia. Photoluminescence analysis at 10 K on as-synthesized powders showed a broad red luminescence around 668 nm under UV laser excitation (He-Cd laser, 325 nm). However after annealing process the red luminescence disappears and the typical band edge emission of GaN around 357 nm (3.47 eV) and the UV band were the dominant emissions in the PL spectra.