Fine-sized powders of BaSi3Al3O4N5:Eu2+ phosphors with high stability and improved photoluminescence properties were successfully synthesized by the traditional solid-state reaction method under a reductive atmosphere using BaF2-fluxing additives in the raw powder mixture. The produced phosphors had strong blue emission under excitation in ultraviolet (UV) and vacuum ultraviolet (VUV) light, due to the 4f 5d–4f7 transition of Eu2+ ions. X-ray diffraction, scanning electron microscopy, XANES, and the photoluminescence (PL) spectra under UV and VUV were used to characterize the as-received samples. The experimental results showed that the addition of BaF2 flux improved the crystalline regime and the PL properties of the produced phosphors. Most significantly, it allowed control of the particle size and particle size distribution in the final powders but did not jeopardize the high thermal and chemical stability of the phosphors produced. With the modification of the BaF2 flux, the blue-emitting BaSi3Al3O4N5:Eu2+ phosphors will show excellent packing and coating properties and could be a good candidate for the light-emitting diodes and plasma display panels.