Yellow-emitting Y 2.95 Al 5 O 12 :0.05Ce (YAG:Ce) phosphor particles with high luminescence efficiency under 450nm ultraviolet (UV) excitation were prepared by a heat treatment of submicrometer-sized oxide powder mixture in a reducing atmosphere at 1550°C. Prior to the heat treatment, the oxide mixture was blended with 5wt% of metal halides – BaF 2 , BaCl 2 , NaF, NaCl, and KF – as a flux. It was observed that YAG:Ce particles prepared with fluorine containing flux demonstrated spherical morphology, high photoluminescence properties, and diameters of 5–20μm, whereas those prepared with chlorine were small-sized particles (≤5μm) with relatively low intensity. The highest relative photoluminescence (PL) intensity (∼118%) was obtained for the samples prepared with 5% BaF 2 . A set of rules was established for the formation of spherical YAG:Ce particles in the presence of this flux.