LiCaAlF₆:Eu and LiCaAlF₆:Ce Single Crystals Grown by the Vertical Bridgman Method in a Nonvacuum Atmosphere and Their Optical and Scintillation Properties

Single crystals of LiCaAlF6:Eu and LiCaAlF6:Ce with a diameter of 25.4 mm were grown by the Bridgman method in a nonvacuum atmosphere. The as-grown crystals are highly transparent and crack- and inclusion-free. The X-ray diffraction pattern confirmed a single phase of a trigonal structure with the space group of P3¯ 1c. The effects of a nonvacuum growth atmosphere on optical and scintillation properties and defect structures were studied. The 4f-5d absorption bands of Eu2+ and Ce3+ in the LiCaAlF6 host peak at 300 and 270 nm, respectively. The results of the photoluminescence spectrum and X-ray excited radioluminescence demonstrate that Eu2+ ions dominantly exist in the LiCaAlF6:Eu single crystal with a small amount of Eu3+ ions. Under γ-ray radiation, single crystals of LiCaAlF6:Eu and LiCaAlF6:Ce have light yields of 23,000 ± 2000 and 1000 ± 100 photons/MeV, respectively. Single scintillation decay components of 1.64 μs and 45 ns are evaluated for LiCaAlF6:Eu and LiCaAlF6:Ce, respectively. The defect structures were investigated by using three-dimensional thermoluminescence measurement.