Fabrication And Properties Optimization Of Ce:?Y,Lu,Gd?₃?Al,Ga?₅O₁₂ Scintillation Ceramics With High Light Output And Fast Decay Time

Scintillator is a kind of functional material which can convert high-energy rays or particles into ultraviolet or visible light.It is widely used in medical imaging,high-energy physics,security inspection,space detection and many other fields.With the development of detectors,the new generation scintillation materials are asked to be of high light yield,fast scintillation decay and low cost.Cerium doped lutetium aluminum garnet(Ce:Lu₃Al₅O₁₂)scintillator with the merits of high density,nanosecond fast decay time,high scintillation efficiency has attracted much attention.However,there are some"slow scintillation components"in Ce:Lu₃Al₅O₁₂ single crystals,which limit the scintillation properties improvement.Low temperature fabrication of transparent ceramics is an important way to optimize the"slow scintillation components"and improve the scintillation properties.Based on the Ce:Lu₃Al₅O₁₂scintillation ceramics,the design of material components and advanced ceramic preparation technology are combined and applied in this work.In order to achieve the controllable preparation of cerium doped garnet scintillation ceramics with high light yield,fast decay time and good optical quality,the factors that restrict the optical and scintillation properties of cerium doped garnet ceramics are studied and optimized.The main contents of this paper are as follows:?1?The Ce,Mg:Lu₃Al₅O₁₂ceramics with the in-line transmittance of 71%@510nm?thickness of 1 mm?were fabricated by the solid-state reaction method combined with vacuum sintering.The annealing temperature and cerium doping concentration were optimized.The increase of air annealing temperature is beneficial to the elimination of oxygen vacancies and the conversion of Ce⁴⁺fast scintillation centers,so as to improve the scintillation properties.However,the increase of annealing temperature will cause the segregation of Al rich secondary phase and have adverse influence on the optical quality of Ce,Mg:Lu₃Al₅O₁₂ceramics.This secondary phase can be attributed to the evaporation of cerium and magnesium elements during the high temperature vacuum sintering.On the other hand,by increasing the doping concentration of cerium ions,the number of luminescence centers increases,which could effectively compete against the defects.However,when the doping concentration of cerium ions is too high?>0.1at%?,it will strengthen the self-absorption effect of cerium ions and affect the luminescence efficiency.?2?Based on the Ce,Mg:Lu₃Al₅O₁₂scintillation ceramics,the Ce,Mg:?Lu,Y?₃Al₅O₁₂ ceramics were designed and fabricated.The effects of Y³⁺on the lattice structure,energy level structure and luminescence properties were studied.The results showes that the cell parameter of Ce,Mg:?Lu,Y?₃Al₅O₁₂ ceramics enlarged linearly with Y³⁺content increasing,which is consist with the Vegard's law.With the increase of Y³⁺content,the conduction band edge of Ce,Mg:?Lu,Y?₃Al₅O₁₂ ceramics is decreasing,meanwhile,some shallow electron traps are approaching to the conduction band and even submerged.By controlling the content of Y³⁺,the shallow electron traps effect is weakened,which can suppress or accelerate the slow components in the scintillation response,and promote the fast scintillation components.After optimization,the light yield of Ce,Mg:Lu_0.5Y_2.5Al₅O₁₂ ceramic sample is achieved to 24 500 ph/Me V with 1?s shaping time.?3?At the same time,a series of work about fabrication,properties investigation and component design of Ce:?Gd,Y,Lu?₃?Al,Ga?₅O₁₂ scintillation ceramics were carried out.Firstly,the Ce:Lu₃Ga₃Al₂O₁₂ scintillation ceramics with pure garnet phase were successfully prepared by the solid-state reaction method combined with oxygen pre-sintering and HIP post-treatment.The Ce:Lu₃Ga₃Al₂O₁₂ ceramics show good steady-state and transient emission efficiency as well as high content of fast scintillation response.However,the thermal ionization effect in the Ce:Lu₃Ga₃Al₂O₁₂ ceramics is significant,which resultes in the energy loss in the processes of photon emission.Therefore,further component optimization and design were carried out.The Ce:Gd₂YGa₃Al₂O₁₂ scintillation ceramics with pure garnet phase were fabricated by the same process as Ce:Lu₃Ga₃Al₂O₁₂ ceramics.These Ce:Gd₂YGa₃Al₂O₁₂ ceramics show the nanosecond fast decay time?56 ns?,high light yield?45 000 ph/Me V at 6?s shaping time?,and good energy resolution?8.67%?.?4?In order to obtain the Ce:Gd₂YGa₃Al₂O₁₂ ceramics with good optical quality and high scintillation properties,the nanopowder with good dispersity and sintering activity was synthesized by the co-precipitation method,and Ce:Gd₂YGa₃Al₂O₁₂transparent ceramics were further fabricated by oxygen pre-sintering and HIP post-treatment.The microstructure evolution of Ce:Gd₂YGa₃Al₂O₁₂ ceramics during pre-sintering and HIP post-treatment was studied.The results show that the pre-sintered ceramics with fine grains,high density,few residual intergranular pores,no interconnected pores and no intragranular pores are the important basis for fabricating the transparent Ce:Gd₂YGa₃Al₂O₁₂ ceramics after HIP post-treatment.By regulating the sintering processes,including the pre-sintering temperature,the pre-sintering time and HIP post-treatment temperature,the type of pores,the number of residual pores and the grain size of ceramic samples can be controlled.After the optimizing of sintering conditions,the fabricated Ce:Gd₂YGa₃Al₂O₁₂ ceramics show the good transmittance?61%@520 nm?,high light yield?37 500 ph/Me V at 10?s shaping time?,fast scintillation decay?61 ns?and good X-ray imaging performance.