Fabrication And Properties Of Eu:?Lu,Gd?₂O₃ Scintillation Ceramics For Radiation Detectors

The Scintillation materials are kind of luminescent materials that can convert high energy rays and ions into ultraviolet-visible light.They play an important role in the fields of detection,nuclear physics and medical imaging.Scintillation materials,with high density,high light output,fast decay time and high radiation hardness etc.,have been widely investigated by the researchers.The Lu-based scintillation materials have gained a lot of attention due to their high density and effective atomic number.Many Lu-containing garnet materials such as Lu₃Al₅O₁₂?LuAG?and Lu₂SiO₅?LSO?have been commercialized.On the other hand,scintillation materials with high output have advantages over others,and their imaging resolution and energy resolution for radiation detectors are better.Eu:Lu₂O₃ scintillation ceramics with both excellent properties mentioned above were introduced by A.Lempicki et al.According to the report from A.Lempicki et al,compared with X-ray powder screen,Eu:Lu₂O₃scintillation ceramics used in X-ray imaging have a higher density and its imaging is clearer.Eu:Lu₂O₃ scintillation ceramics are more economical when compared with Eu:Lu₂O₃ single crystal.Many studies on Eu:Lu₂O₃ scintillation ceramics were reported.Soon after,the studies on Eu:Lu₂O₃ scintillation ceramics are transformed from single component to multi-component,namely Eu:?Lu,Gd?₂O₃ scintillation ceramic were introduced.Z.M."Seeley et al and Rétot Hélène have reported multi-component Eu:?Lu,Gd?₂O₃ ceramics with higher light output and lower afterglow.It is difficult to fabricate highly optical quality Eu:Lu₂O₃ scintillation ceramics and multi-component Eu:?Lu,Gd?₂O₃ scintillation ceramics,and many properties of both ceramics are not clear yet,which limit the application of the both ceramics.Domestic studies on Eu:Lu₂O₃ scintillation ceramics and multi-component Eu:?Lu,Gd?₂O₃ scintillation ceramics are less,and focus on nanopowders.The domestic fabrication technology of transparent ceramics is slightly worse than that of large foreign companies and research institutions.Lacking both ceramics with highly optical quality,domestic research staffs are unable to investigate clearly.After researching deeply,the graduate thesis topic about fabrication and properties of Eu:?Lu,Gd?₂O₃ scintillation ceramics for radiation detectors was put forward.The master's thesis includes three sections.The first part of the master's thesis:multi-component scintillation ceramics fabrication is difficult,so this experiment firstly explored the single-component Eu:Lu₂O₃ scintillation ceramic fabrication technology.On the basis of single-component system,the Gd ions were introduced into Eu:Lu₂O₃lattice.It is necessary to solve two key problems in the fabrication of transparent ceramics with high optical quality.The first is the raw powders with suitable sinterablity.The second is suitable sintering process and process parameters.In the master's thesis,the transparent scintillation ceramics were vacuum sintered from self-made ceramic powders synthesized via co-precipitation method using AHC as the precipitant.The effect of NH₄HCO₃/metal ions molar ratio on chemical composition and microstructure of the precursors and calcined powders have been investigated.The results showed that the chemical composition and microstructure of the precursors with different R value are similar,and R value has a big influence on morphology of the calcined powders.The effect of calcination temperature on crystallinity and mean crystalline size of calcined powders were investigated.The results showed that the crystallinity of the calcined powders become better with the increase of calcination temperatures.The powders calcined at 1100? showed the best dispersity,and the mean crystalline size is about 68 nm.The effect of NH₄HCO₃/metal ions,vacuum sintering temperature on the optical quality and microstructure of ceramics were investigated.The ceramics showed the highest transmittance when R value is 4.0 and sintering temperature is 1825?.The second part of the master's thesis:annealing is helpful to improve the performance of ceramics.Therefore,the effects of annealing on the performance of Eu:Lu₂O₃ scintillation ceramics were investigated.In-line transmittance of the annealed ceramics decreased because of expansion of micro-pores.It is found from the absorption spectra of unannealed and annealed ceramics that the absorption of interstitial oxygen ions showed in the different absorption curve,indicating that interstitial oxygen ions generated during the annealing process.The intensities of all excited peaks and emission peaks of the annealed ceramics are stronger than that of unannealed one,which is related to the elimination of oxygen vacancies.Compared to the light output of commercial BGO,the light output of unannealed Eu:Lu₂O₃scintillation ceramics is 10 times higher than that of BGO.The Eu:Lu₂O₃ scintillation ceramics with different Eu concentrations were fabricated by similar method and technology parameters.The effects of Eu concentrations on microstructure,spectral properties and excitation mechanism of the Eu:Lu₂O₃ scintillation ceramics were investigated.The results showed that the cell constant of Eu:Lu₂O₃ scintillation ceramics increased with the increase of Eu concentration.The crystal structures of Eu:Lu₂O₃ concentration series are cubic.The excitation mechanism is independent of the Eu concentrations and excitation wavelength.The photo-luminescence intensity and radio-luminescence intensity are increased with the increase of Eu concentrations when Eu concentration is below 3at%.The both intensity decreased when the Eu concentration is over 3at%,and it is related to the nonradiative processes.The third part of the master's thesis:on the basis of fabrication of single component Eu:Lu₂O₃ scintillation ceramics,the multi-component Eu:?Lu,Gd?₂O₃scintillation ceramics were successfully fabricated.The influences of vacuum sintering temperature on the microstructure and in-line transmittance of Eu:?Lu,Gd?₂O₃ scintillation ceramics were investigated.Compared with single component Eu:Lu₂O₃ scintillation ceramics,the luminescence decay of Eu:?Lu,Gd?₂O₃ scintillation ceramics is decreased.The photo-luminescence intensity and radio-luminescence intensity of Eu:?Lu,Gd?₂O₃ scintillation ceramics are increased.According to integral intensity of both Eu:Lu₂O₃ and Eu:?Lu,Gd?₂O₃scintillation ceramics,the light output of Eu:?Lu,Gd?₂O₃ scintillation ceramics is 30times higher than that of BGO.