Research On The Growth And Scintillation Properties Of Ce³⁺:Cs₂LiLa_xY_1-xCl₆ Crystals For Neutron Detection

Elpasolite family of Cs₂LiYCl₆:Ce³⁺（CLYC）and Cs₂LiLaCl₆:Ce³⁺（CLLC）scintillation crystals are a new class of neutron detection materials.In this paper,Cs₂LiLaCl₆:Ce³⁺,Cs₂LiYCl₆:Ce³⁺and Ce³⁺:Cs₂LiLa_xY_1-xCl₆（0<x≤40%）crystals have been focused on research work.The preparation method of raw materials for crystal growth was preliminarily explored.Ce³⁺:Cs₂LiLa_xY_1-xCl₆ crystals were successfully grown using the vertical Bridgman technique,and its scintillation properties and mechanism were also analyzed.1.The preparation methods of dehydration experiment with glacial acetic acid as ligand to prepare anhydrous lanthanum chloride,polycrystalline materials of CLYC crystal prepared by liquid phase evaporation and CLLC crystal by liquid phase interface shift method were preliminarily explored.2.Research on growth and properties of CLLC and CLYC single crystals.Transparent CLYC crystal with good crystallization quality and semi-transparent CLLC crystal were grown by vertical Bridgman technique.It is first reported that the melting point of CLLC crystal is 471℃.CLLC crystal belongs to the same cubic structure as CLYC.The reasons for the translucency of the CLLC crystal are explained,and the component segregation occurs during the crystallization process,accompanied by the precipitation of Cs₃LaCl₆ and LiCs₂Cl₃impure phases,and the phase transition of LiCs₂Cl₃ compounds takes place at 418℃.The luminescence and scintillation properties of the two crystals were characterized and analyzed.There are three scintillation mechanisms in CLLC and CLYC crystals,which are core-to-valence luminescence（CVL）,the energy transitions of Ce³⁺5d→4f luminescence,and self-trapped exciton emission（STE）,respectively.The scintillation decay time of CLLC crystal,excited with 662 keVγ-rays from a ¹³⁷Cs source,is 2.7ns,163.2ns and 1171.1ns,respectively.The hygroscopic CLYC crystal exhibits good optical homogeneity and its optical transmittance is more than 70%.The luminescence intensity in hygroscopic CLYC crystal is greatly weakened under x-ray excitation.The energy resolution of CLYC crystal,excited by ¹³⁷Cs gamma ray,is 9.3%.3.Study on growth and properties of Ce³⁺:Cs₂LiLa_xY_1-xCl₆（0<x≤40%）mixed crystals.The crystals of Ce³⁺:Cs₂LiLa_xY_1-xCl₆（0<x≤40%）were grown by vertical Bridgman method,and there are different degrees of cracking in the mixed crystals of different components.The crystalline quality of the component crystal with x=10%is relatively good,and its 2 mm thick wafer is transparent.Ce³⁺:Cs₂LiLa_xY_1-x-x Cl₆（0<x≤40%）crystals belong to the same cubic structure with space group Fm3m as CLYC.Cs₃LaCl₆ impurity phases were observed in Ce³⁺:Cs₂LiLa_xY_1-x-x Cl₆（x=40%）crystal owing to the component segregation during crystallization.The Ce³⁺:Cs₂LiLa_xY_1-xCl₆（x=10%）crystal shows good optical uniformity in the wavelength range of 200-800 nm,and its optical transmittance is greater than 70%.Comparing to the luminescence and scintillation properties of mixed crystals with different components,it is found that the photoluminescence decay time of x=10%component crystal withτ=35.9 ns is the shortest under the excitation of 310 nm.The luminescence intensity of x=10%component crystal is the largest under x-ray excitation.The scintillation decay is the fastest in the component crystal with x=10%,and the fast-decay component is 34.1ns and the slow-decay component is 342.8ns,under the excitation of ¹³⁷Cs gamma source.The calculated energy resolution is 10.3%in the component crystal with x=10%under ¹³⁷Cs source excitation.