The quasi-binary phase diagram BaF2-BaBr2 and its relation to the x-ray storage phosphor BaFBr : Eu2+

In order to understand the formation and stoichiometry of the x-ray storage phosphor BaFBr : Eu 2+ , the phase diagram of the quasi-binary BaF 2 -BaBr 2 system has been investigated. The phase diagram was obtained by means of differential thermal analysis and temperature controlled x-ray diffraction experiments. The resulting phase diagram indicates that BaFBr forms a compound with no detectable solid solubility for neither BaF 2 nor BaBr 2 . Experiments to obtain non-stoichiometric BaFBr via the synthesis route using BaF 2 and NH 4 Br as proposed in the literature could not be verified. It will be shown that the type of colour centre created during x-ray irradiation is related to the non-stoichiometry of the starting compositions before sintering. A surplus of either barium fluoride or barium bromide during sintering allows the controlled formation of F(Br - )- and F(F - )-centres, respectively.