Spherical particles of a rare earth activated barium fluoride halide phosphor precursor having the formula(I) :
Ba1-aMIIaFX : yMI, zLn (I)
[in which MIIis Ca or Sr; MIis Li, Na, K, Rb or Cs; X is Cl, Br or I; Ln is a rare earth element; and a, y and z are numbers satisfying the conditions of 0≦a≦0.5, 0≦y≦0.05, and 0
