LiCaAlF<sub>6</sub>:Eu and LiCaAlF<sub>6</sub>:Ce Single Crystals Grown by the Vertical Bridgman Method in a Nonvacuum Atmosphere and Their Optical and Scintillation Properties
Mei Yang, Matthew Loyd, Jian Lin Shi, Huanying Li, Xiangyong Zhao, Guohao Ren, Charles L. Melcher, Yuntao Wu
Abstract
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 P3̅1c. 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.