Research On The Growth And Properties Of New Material Ce:Cs₂LiLaCl₆ Crystal For Neutron Detection

Elpasolite family of Ce³⁺:Cs₂LiLaCl₆（CLLC）scintillation crystals is a new class of neutron detection materials.In this paper,research on growth and properties of Ce:Cs₂LiLaCl₆and Ce:Cs₂LiLa_xY_（1-x）Cl₆（0.5≤x≤0.7）crystals will be reported.The series of crystals were grown by the vertical Bridgman technique,the growth method was improved and the luminescence mechanism and scintillation properties were analyzed.1.Optimization and characterization of CLLC crystal growth method.Using vertical Bridgman technique to grow transparent CLLC crystals with good quality.To solve the problems of the appearance of Cs₃LaCl₆ impurity phases during the growth of CLLC crystals,additional Li Cl were added into the raw materials for crystal growth.The crystal quality is the best when Li Cl is over 10%.Core-to-valence luminescence（CVL）,the energy transitions of Ce³⁺5d→4f luminescence and self-trapped exciton emission（STE）is the scintillation mechanisms of CLLC crystals,respectively.With the monitoring wavelength of 400 nm,the peaks of the excitation spectra were fitted to be centered at 220 nm,264 nm,319 nm,336 nm and 355 nm,which correspond to the transitions from the lowest sublevel ²F_5/2 to t_2g and e_g sublevels of Ce³⁺ions.The peaks of the emission spectra were fitted to be centered at 373 nm and 404 nm,which correspond to the transitions from the lowest sublevel of t_2gto the ²F_7/2 and ²F_5/2sublevels of Ce³⁺ions.In the X-ray excited emission spectra,the CVL peak was located at 302 nm.The decay time was 36.6 ns in CLLC crystal doped with 0.5%Ce³⁺.The transmittance of?11×3 CLLC crystals at 400 nm reached 61%.The light output of CLLC crystals under ¹³⁷Cs gamma ray excitation is 28000 ph/Me V,the energy resolution is 7.2%,and the decay time is 179 and 1491 ns,respectively.The Energy resolution is 3.1%under the excitation of a moderated ²⁵²Cf neutron source.2.Growth and properties of CLLC crystals with different concentrations of Ce³⁺.CLLC crystals with different concentrations of Ce³⁺were grown by vertical Bridgman technique.The photo-luminescence properties of the CLLC crystals were characterized and analyzed.Excitation and emission peaks of 0.5%Ce³⁺:CLLC crystal are located at 348 nm and 372 nm,and the decay time is36.6 ns.Excitation and emission peaks of 5%Ce³⁺:CLLC crystal are located at 312-370 nm and 389nm,and the decay time is 39.1 ns.Excitation and emission peaks of 0.5%Ce³⁺,0.2%Pr³⁺:CLLC crystal are locate at 354 nm and 382 nm and the decay time of is 30.8 ns.3.Growth and luminescence properties of Ce:Cs₂LiLa_xY_（1-x）Cl₆（0.5≤x≤0.7）mixed crystals.The crystals of Ce:Cs₂LiLa_xY_（1-x）Cl₆（0.5≤x≤0.7）were grown by vertical Bridgman method.Excitation and emission peaks of Ce:Cs₂LiLa_0.5Y_0.5Cl₆ crystal are located at 319-360 nm and 404nm,and the decay time of Ce:Cs₂LiLa_0.5Y_0.5Cl₆ crystal is 36.4 ns.Excitation and emission peaks of Ce:Cs₂Li La_0.6Y_0.4Cl₆ crystal are located at 319-360 nm and 417 nm,and the decay time of is 38.7 ns.Excitation and emission peaks Excitation peak of Ce:Cs₂LiLa_0.7Y_0.3Cl₆ crystal are located at 344 nm and 404 nm,and the decay time is 36.3 ns.