| Scintillation crystals can be used for the detection of X-rays,?-rays,neutrons and other high-energy particles.Detection and imaging technologies based on scintillation crystals have been used in a wide range for Medical,high-energy physics,industrial inspection,satellite detection,industrial nondestructive inspection,safety inspection.In terms of chemical composition,inorganic scintillation crystal materials include oxides and halides(iodide,bromide,chloride,fluoride).Among them,iodide scintillation crystals have attracted widespread attention due to their high light output,large atomic number,extremely low energy resolution,and small afterglow time.However,these iodide scintillation crystals have the characteristics of being easily deliquescent,which brings great inconvenience to the growth and processing.The traditional method of growing iodide scintillation crystals is Bridgeman method.In this method,the raw material is placed in a closed quartz tube,and the crystal is grown by setting a temperature program,which can effectively prevent the deliquescent of the crystal and achieve the growth of a large bulk crystal.Although good quality iodide crystals can be grown by the Bridgeman method,its disadvantage is that it can not grow crystals in stereotypes,which will cause a large amount of crystal loss during processing applications,and complicated processing procedures may increase the deliquescence of the crystals.Therefore,if stereotyped growth can be achieved,it will facilitate the practical application of halide scintillation crystals.Based on the consideration of stereotyped growth of halide crystals,the Edge-defined Film-fed Growth(EFG)method has attracted our attention.This method can not only realize the stereotyped growth of the crystal,but also have a faster growth rate.The EFG method plays an important role in the development of shaped crystals and has been widely used in the growth of traditional oxide crystals,such as sapphire.However,there are few studies on the growth of halide scintillation crystals using EFG methid,and the related work is facing many difficulties.First,the pulling operation needs to be implemented in a closed device,and the crystal growth process needs to be observed in real time.Therefore,the design of the growth furnace?the growth device in the furnace?the temperature field and the die are all major difficulties to be overcome.Led by the major demand in the field of scintillation crystals,taking the "growth of halide scintillation crystals by EFG method" as the PhD project,aiming at solving the growth device,exploring the experimental conditions and optimizing the crystal quality.This thesis systematically studied the growth of CsI-SrI2 system crystals.CsSr1-xEuXI3(x=0.03,0.05,0.07)crystals,CsSr1-xPrXI3+x(x=0,0.01,0.03,0.05)and CsSrBrI2:5%Eu crystals were grown by EFG method for the first time.In addition,its optical properties were studied.The main research contents and conclusions of this paper are as follows:I.Design of the device used for crystal growth by EFG method.This thesis explores the growth of halide crystals by EFG method in detail.An experimental furnace and quartz sealed growth device for crystal growth were designed.On the basis of designing a closed growth device,a component for pulling operation in the sealing device was also designed.Based on the research on the growth furnace,a temperature field suitable for crystal growth was designed.Based on theoretical calculations,a die for crystal growth by EFG method was designed.By debugging the experimental device,the air intake and exhaust systems during the crystal growth process was designed.In order to improve the quality of the growing crystals,a device for filtering raw materials was designed.II.Growth and optical properties of SrI2:Eu crystal.SrI2:5%Eu single crystal was successfully grown by EFG method with a growth rate of 5 mm/h,and the crystal size reaches ?10 mm×100 mm.The influence of temperature field on the quality of crystal and the method of obtaining seed crystal were explored.The experimental operation of the crystal growth by EFG method is studied.The basic optical properties of the crystal were studied.The results show that Eu2+ions can enter SrI2 matrix lattice uniformly to replace Sr2+,and no Eu3+ was obscrved.III.Growth and optical properties of CsSrI3:Eu crystal.In order to verify the generality of the growth device,we successfully grown binary CsSr1-xEuxI3(x=0.03,0.05,0.07)crystals by EFG method for the first time,the growth rate reached 12 mm/h,and the crystal size were ?10 mm×55 mm(CsSrI3:3%Eu),?10 mm×50 mm(CsSrI3:5%Eu)and ?10 mm×45 mm(CsSrI3:7%Eu).The device and method of crystal synthesis were explored.The factors affecting the quality of the crystals were studied,such as temperature field,material filtration,growth rate,etc.The optical properties of the crystals were studied.The fluorescence performance data of CsSr1-xEuXI3(x=0.03,0.05,0.07)crystals showed that the 4f-5d emission band of Eu2+ ions was observed at 451-454 nm.When the Eu2+ concentration reached 7%,a concentration quenching phenomenon was observed.The decay time of CsSrI3:3%Eu is 1.32 ?s,CsSrI3:5%Eu is 1.35 ?s,and CsSrI3:7%Eu is 0.73 ?s.The deliquescent properties of CsSrI3 crystals were studied.IV.Growth and optical properties of CsSrI3:Pr crystal.CsSr1-xPrxI3+x(x=0,0.01,0.03,0.05)single crystals were grown by EFG method for the first time,the growth rate reached 12 mm/h,and the crystals size were ?10 mm×85 mm(CsSrI3),?10 mmx30 mm(CsSrl3:1%Pr),?10 mm×25 mm(CsSrI3:3%Pr)and ?10 mm×25 mm(CsSrI3:5%Pr).The factors that affect the quality of the crystals during the growth process were discussed,such as the quality of the seed crystal and the stability of the temperature field.The optical properties of the crystals were studied.The fluorescence data showed that an emission peak of Pr3+ was observed at 442 nm.Compared with the CsSrI3:Eu crystal,the emission range shifts significantly toward the short wavelength direction,and the excitation range becomes wider as the Pr3+ ion concentration increases.The fluorescence decay time of CsSrI3:1%Pr3+ is 0.78 ?s,CsSrI3:3%Pr3+is 0.81?s,and CsSrI3:5%Pr3+is 0.87 ?s.In addition,compared with CsSrI3:Eu,Pr3+doped CsSrI3 crystals can reduce the decay time.Therefore,we believe that the luminescence performance of CsSrI3:Pr may be better than that of CsSrI3:Eu crystal.V.Growth and optical properties of CsSrBrI2:Eu crystal.CsSrBrI2:5%Eu crystal was successfully grown by EFG method for the first time,the growth rates reached 12 mm/h,and the crystal size was ?10 mm×50 mm.We replaced some iodine ions with bromine ions in an attempt to improve the deliquescent and luminescence properties of the CsSrI3:Eu crystals.The fluorescence data of CsSrBrI2:5%Eu crystal showed that the emission peak range of CsSrBrI2:5%Eu crystal is enlarged relative to CsSrI3:Eu,and the fluorescence lifetime has increased. |
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