Study On The Phase Separation And Scintillation Properties Of Cs₂LiLaBr₆: Ce Crystal

Due to their excellent properties under various types of radiation excitation,Ce-doped scintillators have been widely used in many fields,such as medical diagnosis,nuclear detection,and high-energy particle physics.Elpasolite crystals are a new class of inorganic scintillators that can detect and distinguish gamma rays and neutron radiation.For example,Ce-doped Cs₂Li YCl₆（CLYC）,Cs₂Li La Cl₆（CLLC）,and Cs₂Li YBr₆（CLYB）have been investigated in the last two decades.Cs₂Li La Br₆:Ce（CLLB:Ce）is a novel elpasolite scintillator that has attracted great interest in radiation detection applications.It has excellent gamma-neutron dual readout capability and is a promising potential commercial product.As has been reported for many elpasolite crystals,it is difficult to obtain large-diameter CLLB:Ce single crystals directly from a stoichiometric melt because of incongruent melting.Typical as-grown ingots only contain a small middle portion of single-phase CLLB when grown with stoichiometric raw materials.An excess of Li Br may be necessary for the CLLB:Ce crystal growth,but no detailed studies on this crystal have been reported.In this paper,the vertical Bridgeman method is used to grow CLLB:Ce crystals with the non-stoichiometric batching method.It was found that excess Li Br contributed to the growth of CLLB:Ce crystals.The CLLB:Ce crystal with a large diameter was successfully obtained,and the transparent single crystal portion occupied almost the entire middle of the grown crystal.The scintillation performance was characterized,and the CLLB:Ce crystal with excellent comprehensive properties was successfully obtained.The main results of this paper are as follows:（1）CLLB:Ce crystals with dimensions of 0.5"and 1"were successfully prepared by the vertical Bridgman method.（2）By comparing the growth of different raw material ratios,it was confirmed that excess Li Br is beneficial to improve the quality of CLLB:Ce crystals.The XRD,DSC-TG,and FAAS test results of the crystal samples show that phase separation occurs during the growth of CLLB:Ce crystals.At the beginning of crystal growth,the main phases are CLLB and Cs₃La Br₆.In the middle,the main phase is CLLB.The main phases in the final stage are CLLB and Li Br.The crystallization behavior of the growth process is very complicated.（3）The UV-Vis fluorescence spectra of the CLLB:Ce crystal shows that the main emission peak positions of the crystal are 390 nm and 420 nm,respectively,corresponding to the 5d→4f transition emission of Ce³⁺.The main excitation peaks of CLLB:Ce crystals are located at 281 nm and 360 nm,respectively,which belong to the characteristic absorption of Ce³⁺.In particular,with the increase of Ce³⁺doping concentration,the intensity of the crystal excitation peak and the emission peak are enhanced;the X-ray excitation-emission spectrum of the CLLB:Ce crystal shows that the crystal has two main emission peaks,which are 393 nm and 421 nm,corresponding to the 5d→4f^{1 2}F_5/2 and 5d→4f^{1 2}F_7/2 transition emissions at Ce³⁺are consistent with the UV-Vis fluorescence spectrum.（4）Theγ-ray test results of CLLB:Ce crystals show that the light output of this crystal can reach 48,000 ph/Me V,its energy resolution is 4.0%,and its performance has reached the mainstream level of this crystal reported internationally,which indicates that CLLB:Ce crystal is a very promising new type of elpasolite crystals.（5）The Cs₃La Br₆ and Cs₂La Br₅ samples were synthesized by experiments,which are in good agreement with their corresponding standard cards.The fluorescence spectrum shows that the Cs₃La Br₆ emission peak consists of two peaks at 433 nm and 465 nm,and the excitation peaks are at 287 nm and 354 nm.The Cs₂La Br₅emission peak consists of two peaks at 358 nm and 378 nm,and the excitation peaks are at 254 nm and 300 nm;The moisture absorption experiment showed that Cs₃La Br₆ had the weakest moisture absorption,and La Br₃ and CLLB:Ce had stronger moisture absorption.Cs₃La Br₆ does not need to be sealed for testing samples.