We studied the mechanism for the formation of cerium-activated barium fluoride scintillation ceramics and especially X-ray luminescence of its powdered precursors, prepared by co-precipitation of barium and cerium fluorides from aqueous solutions. We have found that the Ce3+ luminescence, which is typical for cerium (III)-containing ceramics and single crystals, was not observed for such polycrystalline precursors, and the intensity of barium fluoride’s own luminescence decreases with increasing amounts of the cerium dopant in the specimens. We have interpreted our results as two-phase precipitation of barium hydrofluoride (BaF2·HF) and cerium fluoride, respectively. Cerium (III) became incorporated in fluorite-type barium fluoride lattice only later, in the course of ceramics synthesis by the hot-pressing technique.