RbBr and CsBr doped with Eu²⁺ as new competitive X-ray storage phosphors

After X-irradiation of the alkali halides RbBr and CsBr doped with divalent Eu a significant photostimulated luminescence (PSL) effect was found. In both systems the electron trap centre is an F centre, the hole trap centre is still unknown. The Eu²⁺ aggregation with cation vacancies plays an important role. Although all of the different Eu²⁺ aggregates seem to show PSL effects, they have different PSL efficiencies, decay times and spectral characteristics. In the case of RbBr:Eu²⁺ it was possible to investigate the different Eu²⁺-cation vacancy aggregate states by magnetic circular dichroism of the optical absorption (MCDA) and MCDA-detected electron paramagnetic resonance. In Eu²⁺-doped CsBr no paramagnetic Eu²⁺ aggregate nor isolated Eu²⁺ was found, in spite of intense and typical Eu²⁺-related PSL effects.