Fabrication And Performance Modulation Of Praseodymium Doped Lutetium Aluminium Garnet Scintillation Ceramics

Scintillators can emit ultraviolet or visible light after absorbing high-energy rays or particles.The detection of high-energy particles and rays can be realized by combining the scintillator with the back-end photoelectric devices.Therefore,scintillators are widely used in medical imaging,high-energy physics,land security,geological exploration,space exploration and many other fields.In recent years,with the rapid development of medical imaging and high-energy physics,more stringent requirements have been put forward for scintillators.Therefore,the development of scintillators with higher light yield,fast decay,high density,high radiation resistance and low cost has become one of the most important tasks of material scientists in recent years.Praseodymium doped lutetium aluminium garnet?Pr:LuAG?scintillator has high density??=6.7 g/cm³?,high effective atomic number(Z_eff=63),ultrashort decay time of 20 ns,high theoretical light yield,excellent light yield nonproportionality and low energy resolution.Siemens assessed that it is one of the two materials with the highest quality factor for TOF-PET technology.However,the existence of slow components in single crystals limits its promotion and application.Transparent ceramics have been proved to be an important way to improve scintillation performance due to their lower fabrication temperature.Current studies have found that the scintillation properties of Pr:LuAG ceramics are very sensitive to sintering additives,so the controllable fabrication and performance modulation of Pr:LuAG transparent scintillation ceramics become very important.Based on the above background,this paper focuses on the fabrication and performance modulation of Pr:LuAG scintillation ceramics.Controllable preparation of Pr:LuAG transparent ceramics has been carried out through various technical paths.The factors that restrict the optical and scintillation properties of the ceramics were systematically studied.On this basis,the performance modulation and structure design were carried out.The main contents of this paper are as follows:?1?Pr:LuAG scintillation ceramics were prepared by the vacuum reaction sintering method.The sintering technology was explored and the suitable sintering mechanism was determined.1 mm thick Pr:LuAG transparent ceramics with transmittance of more than 72%in the visible region were prepared using trace MgO as sintering aid.Pr³⁺was oxidized into Pr⁴⁺in the air annealing process with Mg additive.However,the charge transfer absorption from coordination oxygen to Pr⁴⁺overlapped with the emission band of Pr³⁺which caused self-absorption in the material and seriously deteriorated the scintillation properties of Pr:LuAG.In order to avide the formation of Pr⁴⁺,the effect of SiO₂ additive on the optical and luminescent properties of Pr:LuAG was studied.The results showed that the transparency of ceramics was difficult to be achieved by adding a little SiO₂,but too much SiO₂ additive would introduce charged defects and deteriorate the scintillation performance.?2?In order to avoid the influence of sintering additives,the technology of preparing Pr:LuAG transparent ceramics by vacuum reactive sintering without sintering additives was explored.The effects of stoichiometry on the densification,optical and scintillation properties of Pr:LuAG ceramics were studied.It was found that excessive Lu could effectively inhibit grain growth,promote pore elimination and work as sintering aids.The 1 mm thick Pr:LuAG transparent ceramics with a transmittance of more than 55%were obtained.The effect of doping concentration on the scintillation properties of Pr:LuAG ceramics was studied,and the highest light was 6900 ph/MeV with 1?s shaping time.It was found that high concentration of Pr doping could suppress the slow scintillation component and achieve effective modulation of the timing properties.The inside mechanism was analyzed by low temperature thermoluminescence.In addition,bilayer garnet ceramic scintillators for Phoswich depth detection were first proposed and fabricated.The results of fluorescence and scintillation show that the composite ceramics with garnet structure have depth detection ability and are suitable for wavelength and pulse shape discrimination technology.This structure can be further extended to other matrix ceramic scintillators.?3?In order to further promote the optical quality of ceramics and avoid the antisite defects caused by excessive Lu,Pr:LuAG transparent ceramics were obtained by pre-sintered by the vacuum reactive sintering combine with hot isostatic pressing.The effects of vacuum pre-sintering conditions and SiO₂ content?less than 200 ppm?on the microstructures of pre-sintered and hot isostatic pressed Pr:LuAG ceramics were studied.It was found that small amount of SiO₂ can effectively promote the elimination of pores and significantly improve the optical quality of ceramics.The transmittance in the visible region of 1.2 mm thick ceramics was over 77%.The light yields of Pr:LuAG ceramics with 150 ppm SiO₂ additive exceeded 13000 ph/MeV with 1?s shaping time,which has exceeded some Pr:LuAG single crystals.The influence of SiO₂ on the light yield of Pr:LuAG ceramics was less than 16%and the energy resolution was improved.On this basis,by using the idea of energy band engineering,Lu was partly replaced with Y,the transparent Pr:LuYAG ceramics with transmittance of more than 80%in the visible region were obtained and the light yield greatly increased by 57%.Thermoluminescence results showed that the lower conduction band bottom buried some shallow defects is the main reason of the performance improvement.?4?In order to completely abandon sintering additives and pursue higher optical quality,Pr:LuAG nanopowders were prepared by the co-precipitation method.The influences of the amount of precipitant and calcination temperature of precursors on the composition,morphology and dispersion of the nanaopowders were studied.1 mm thick Pr:LuAG transparent ceramics with transmittance of more than 72%in the visible region were prepared by vacuum sintering.Too much or too little precipitant is not conducive to the improvement of dispersion and purity of Pr:LuAG nanopowders;in addition,the inconsistent dissolution of precursors in the washing process would lead to the deviation of stoichiometry of the nanopowders and form Al-riched second phase in the ceramics.After optimizing the preparation conditions,Pr:LuAG transparent ceramics with transmittance over 81%in the visible region were obtained.The light yield of resulting Pr:LuAG ceramics was 7086 ph/MeV.Ca²⁺impurity in the raw materials introduced Pr⁴⁺and limited the improvement of scintillation properties.