Physical bromine storage

Safety risks and the environmental impact are of major importance for the practical success of bromine storage system. The nonaqueous polybromide complexes in general show excellent physical properties, such as good ionic conductivity (0.1-0.05 Qcirf1), oxidation stability (depending on the nature of the ammonium ion), and a low bromine vapor pressure. The concentration of active bromine in the aqueous solution is reduced by formation of the complex phase up to 0.01-0.05 mol/L, hence ensuring a decisive decrease of selfdischarge. 

It has been found that only the bromine F centers contribute to the photostimu-lability, although the X-ray irradiation creates both fluorine and bromine F centres [18]. These authors have also derived estimates of the concentrations of defect centers in a particular BaFBr Eu- sample. Even if these values arc not very reliable, they illustrate how complicated the physical mechanisms in a storage phosphor may be 82% of the centers created by irradiation are fluorine F centers or variants therebf these do not contribute to the photostimulable luminescence. The remaining 18% of the created centers are bromine F centers. Of these about one quarter arc spatially correlated to the hole center and the Eu ion, i.e. they yield PSL via a tunelling mechanism the others are not correlated and need thermal activation via the conduction band in order to yield PSL. These estimated concentrations depend strongly on the history of the sample and on the Eu concentration. 

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