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Divalent cation codoping, such as with Ca2+and Mg2+, is beneficial for the scintillation performance enhancement of Czochralski-grown Lu2SiO5:Ce (LSO:Ce) single crystals for nuclear medical imaging applications, but with that benefit comes a tendency toward acentric growth due to the reduced surface tension of the melt. Here, we present a divalent Cu codoping strategy to achieve a simultaneous improvement of light yield, energy resolution, scintillation decay, and afterglow in LSO:Ce single crystals without destabilizing the solid–liquid interface or promoting acentric growth. High-quality 32-mm-diameter and 110-mm-long LSO:Ce single crystals codoped with 0.1 and 0.3 atom % Cu2+ions in the melt were successfully grown using the Czochralski method. While the surface tension of the LSO melt does decrease with Cu2+codoping, analogous to the effect of Ca2+codoping, it is not reduced enough to affect the crystal growth stability or diameter control. With 0.1 atom % Cu2+codoping, the scintillation light yield of LSO:Ce can be significantly enhanced from 32 000 to 39 000 photons/MeV with an improved enegy resolution of 9% at 662 keV, and a reduced afterglow at room temperature. A continuous shortening of scintillation decay time with Cu2+codoping is ascribed to the combined effect of enhanced thermal ionization from the Ce3+5d1state and a reduction of the emission contribution from Ce2 centers, i.e., in the site neighboring six oxygens. Thermoluminescence and afterglow measurements are utilized to study the defect structure and explain the variation in scintillation yield.

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.