Highly luminescent GaN powders have been synthesized by reacting high purity gallium metal with ultra-high purity ammonia in a horizontal quartz reactor at 1100°C. The powders produced in this reactor consist of light grey micro-crystals with wurtzite structure. Elemental analysis indicates that the powders obtained by this method have a high nitrogen concentration (more than stoichiometric GaN, 16.73 weight %). Powder X-ray diffraction demonstrates that the material has a high purity and single crystalline structure. Electron microscopy shows that the powders consist of at least two kinds of particles, small sized platelets and large sized needles. The resulting GaN powders are thousands of times more cathode- and photo-luminescent than other GaN powders including commercially available material. Their luminescence intensities are comparable to that of GaN thin films grown by hydride vapor phase epitaxy and metal organic chemical vapor deposition.