The formation of Y 3 Al 5 O 12 :Ce 3+ (YAG:Ce) powders from the corresponding submicrometer-sized oxides and 5wt% BaF 2 flux is studied at different heating temperatures. The reaction powders are characterized using XRD, SEM, and TEM-EDS. X-ray analysis reveals the sequential formation of the Y 4 Al 2 O 9 (YAM), YAlO 3 (YAP), and Y 3 Al 5 O 12 (YAG) phases in the temperature range of 1000–1300°C. It is shown that the nucleation process occurs via the dissolution–precipitation mechanism, whereas the grain growth process is controlled via the liquid-phase diffusion route. YAG:Ce phosphor particles prepared using a proposed technique exhibit a spherical shape, high crystallinity, and an emission intensity that is approximately 10–15% greater than that of commercial phosphor powder.