Structure and scintillation of Eu2+-activated calcium bromide iodide

We report the structure and scintillation properties of Eu2+-activated calcium bromide iodide. CaBr0.7I1.3 was the only composition that could be synthesized in the CaBr2-CaI2 system. The compound has an effective atomic number of 47 and crystallizes in a trigonal crystal system with the R-3 space group and a density of 3.93 g/cc. The structure is layered and contains Ca in an octahedral environment with the Br/I anions jointly occupying a single site. Eu2+-activated samples show an intense narrow emission, characteristic of the 5d-4f transition of Eu2+, when excited with UV or X-rays. The sample with 0.5% Eu shows a light output of 63,000 ph/MeV at 662 keV with 96% of the light emitted with a monoexponential decay time of 1332 ns. An energy resolution of 10.4% full width at half maximum (FWHM) has been achieved for 662 keV gamma rays at room temperature.