The Growth And Luminescence Properties Of K₂LaX₅:Ce?X=Cl,Br? Complex Rare-earth Halide Scintillation

Complex rare-earth halides were considered to be potential detection materials.In recent years,the materials such as Cs₃LaCl₆:Ce,,RbGd₂Cl₇:Nd,K₂LaCl₅:Pr were reported in succession.They were be widely applied to medicine,remote sensing,telecommunications,security technology,high-energy physics as fluorescent powder and crystals.Scintillation with excellent properties can be prepared by adding Ce³⁺as luminant into the complex rare-earth halide matrix.X-rays,gamma rays and?particles can be detected with scintillator by crystal radiation transition mechanism.In this paper,We studied about the growth of K₂LaX₅:Ce?X=Cl,Br?complex rare-earth halide scintillation using Bridgman method,the improvement of crystals defects and the scintillation characterization.Discussed advantages of materials structure and properties.The sensitivity of crystals to water was calculated quantitatively.The research work is mainly divided into the following three parts.1.K₂LaCl₅:Ce crystal growth and properties characterization.The raw materials of crystals such as KCl powder were pretreated to remove water and other impurities.The K₂LaCl₅:Ce polycrystalline materials were prepared by the traditional high temperature solid synthesized method.According to the XRD analysis,the curve showed the crystal structure was orthorhombic structure,the cell parameters were a=12.745?,b=8.868?,c=8.018?and the cell volume was906.2?³,which could well match with the standard PDF card.The K₂LaCl₅:Ce single crystal was obtain by Vertical Bridgman method.The crystal was transparent.The transmittance of the crystal sample was close to 90%by measuring of spectrophotometer.There are two excitation peaks of270 nm and 345 nm in the photoluminescence spectrum,due to the electrons transition in Ce³⁺from4f orbit to T_2gg and E_g energy level configuration of 5d orbit.The emission peaks are located at 355nm and 375 nm,which are consistent with peak position of X-ray excitation emission spectrum.Under the excitation of ¹³⁷Cs?ray,the multichannel energy spectrum of crystal was measured,the energy resolution was 5.9%and the scintillation decay time was 23 ns.2.K₂LaBr₅:Ce single crystal was grown with Bridgman method,and the scintillation performances of sample was studied.For the first time,using the quartz crucible which the length of capillary is 20 mm and the diameter of pipe is 12 mm to seal the crystal material.After the crystal growth process,the crystal which owning serious cracking was obtained,Moreover,there were many white inclusion on the surface of the crystal.It was difficult to gain the large size of the complete single crystal.In the second growth process,the quart crucible with the capillary length of 70 mm and the diameter of 12 mm was used to seal the crystal materials.We adjusted the temperature parameters and show down the rate of decline process.After incision,grinding and polishing processing,the complete single crystal without cracking could be obtained.The crustal surface is foggy,the absorption edge of the crystal in the transmittance spectrum at 350 nm and there is a strong absorption band form 300 nm to 350 nm which caused by the electron transition inner the Ce³⁺form²F_5/2/2 orbit to 5d low-energy configuration.In the X-ray excitation emission spectrum,the fluorescence band of the crystal is mainly from 350 nm to 400 nm,the position of the strongest and the second strongest peak are 360 nm and 385 nm respectively.The optical attenuation curve of K₂LaBr₅:Ce crystal was test by UV excitation source,the result of decay time is 22 ns which shorter than the attenuation time compared to K₂LaCl₅:Ce crystal.The energy resolution of the crystal sample is 8.2%in the gamma ray multichannel energy spectrum.3.K₂LaCl_xBr_5-x:Ce?x=1,2,3,4?mischcrystal growth and scintillation performance characterization.In order to combine the advantages of K₂LaCl₅:Ce and K₂LaBr₅:Ce crystals,a series of K₂LaCl_xBr_5-x:Ce?x=1,2,3,4?mixed polycrystalline materials were synthesized by high temperature solid state method.Using Bridgman method to grow K₂LaCl₄Br:Ce,K₂LaCl₃Br₂:Ce,K₂LaCl₂Br₃:Ce,K₂LaClBr₄:Ce single crystal.The transmittance spectrum,PL spectrum,X-ray excitation emission spectrum,PL attenuation time,gamma ray attenuation time and multichannel energy spectrum were tested.When the ratio of Cl^-and Br^-is 1:4,the maximum intensity of transmittance can reach to 70%.As the increase of the Br^-concentration,the transmittance of crystal is decrease.When the ratio of Cl^-and Br^-is 4:1,the transmittance of crystal is 45%.The peak position of the excitation emission spectrum of X-ray is about 360 nm and 380 nm.Under the multichannel spectrometer test,the energy resolution of four crystal are 13.7%,9.8%,9.1%,9.2%,respectively.The energy resolution is negatively correlated with the thickness of the crystal sample.