Discovery of New Compounds and Scintillators of the A4BX6Family: Crystal Structure, Thermal, Optical, and Scintillation Properties

We report the discovery of four new compounds of Eu2+-doped scintillators [Cs3Rb]SrI6, [Cs3K]SrI6, [Cs3Rb]CaI6, and [Cs3K]CaI6. A compositional engineering strategy dictated by the structural systematics of the base compounds Cs4CaI6and Cs4SrI6(space group R3̅c-hexagonal basis) was conducted to confirm an ideal solid solution for this system. Substitution of smaller monovalent cations Rb1+and K1+for Cs1+, maintained the crystal structure, producing an ordered substitution. Crystals were initially grown doped with 0.5% Eu to compare scintillation properties, and a Eu2+optimization study determined that 7% Eu was the ideal concentration. A 56 mm3crystal of composition [Cs3.5Rb0.5]SrI6:Eu 7% gave the best measured scintillation performance with an absolute light yield of 75 000 ph/MeV and energy resolution of 3.3% at 662 keV.