Fabrication And Properties Of Silicate-based Scintillating Glass And Glass Ceramic With High Crystallinity

As one type of functional materials for measurement of ionizing radiation,scintillators have been widely used in nuclear medicine,homeland security,high energy physics,energy exploration and other fields.Single crystals scintillators have been recognized as the most excellent scintillator materials because of their superior performance.Unfortunately,the fabrication of single crystal scintillators greatly relies on the precise equipment and strict production conditions,which are time consuming and expensive.Glass and glass-ceramics scintillators have become the alternative and promising candidates owing to their flexible chemical composition,microstructures and low cost.Cerium-doped barium disilicate（Ba O-2Si O₂:Ce,DSB:Ce）glass,which can be produced on an industrial scale,has excellent properties such as medium density（3.8 g/cm³）,excellent radiation hardness and thermal stability,etc.It has been applied for oil logging industry and also shows great promise for electromagnetic calorimetric application.However,the light yield of DSB:Ce glass is relatively low,only 100 ph/Me V.The optimization of glass composition and further construction of glass-ceramics have been demonstrated to be the powerful strategies for developing highly efficient scintillators.Especially,the crystallization of glass into glass-ceramics with high crystallinity and dense crystalline domains is expected to greatly improve the scintillating performance.However,the preparation of this type of unique glass-ceramics by glass crystallization process strictly depends on the aerodynamic levitation method,and the sample size is less than 5 mm.These issues greatly limit their practical applications.In this thesis,firstly we make the systematic studies on the glass forming abilities and microstructure-scintillating properties of the Ba O-Si O₂ binary scintillating glass system.Secondly,we study the crystallization process of this glass system and propose the strategy of full crystallization of glass into glass-ceramics with high crystallinity for improving the scintillating properties.As the proof-of-concept experiments,the scintillating glass-ceramics with high crystallinity are successfully fabricated.The corresponding radiation detection devices are constructed and the practical applications for online radiation monitoring and imaging are realized.The results indicate that the proposed cost-effective strategy combines both advantages of easy glass fabrication and excellent optical properties of ceramics,which lays a foundation for the development and practical application of scintillating materials with high performance and low cost.The main contents of the thesis are summarized as follows.（1）Based on the phase diagram of binary Ba O-Si O₂ glass system,a series of Ce-doped Ba O-Si O₂ oxide scintillating glass samples are prepared by the melting-quenching method.The optical property studies indicate that the luminescence properties of the optimized Ba O-Si O₂oxide glass can be greatly improved.Particularly,the X-ray induced luminescence intensity of the glass sample can reach to～2.2 times higher than that of the commercial DSB:Ce glass.The physical mechanism of the improved scintillating performance is discussed.With the decreased content of Ba O,the polymerization degree of glass structure gradually increases and the content of non-bridging oxygen decreases,leading to the reduced probability of the non-radiation transition.In addition,the change in the Ce³⁺/Ce⁴⁺ratio also influences the optical properties and the increase in the relative content of Ce³⁺active centers is supposed to contribute to the improvement in the scintillating properties.Furthermore,it is also found that the density of Ba O-Si O₂ glass had little effect on the scintillating properties.Thus,it can be concluded that the relative content of defects and Ce³⁺ions had great influence on the scintillating properties.The findings provide the valuable reference for the design and preparation of high-performance scintillating glasses.（2）The scintillating glass-ceramics activated with Ce³⁺active centers are fabricated based on the optimized glass system and their optical properties are studied.Through rational control of the heat-treatment procedures including the temperature and duration,transparent glass-ceramics with high crystallinity and regular crystalline domains are successfully prepared by pressureless crystallization.The crystal size is estimated to be～10μm and the crystallinity can reach to as high as～92.4%.The transmittance of the sample is 66.63%at 800 nm.The scintillating properties are studied and the X-ray induced luminescence intensity of glass-ceramics is～5.9 times higher compared with that of the as-made glass.Noting that it is equivalent to that of commercial BGO crystal.The pulse height distribution spectra are measured and the results indicate that the light output of glass-ceramics is about 522 ph/Me V,which is higher than that of the as-made glass（325 ph/Me V）,indicating the great improvement in the scintillating performance.The corresponding physical mechanism is elucidated.It is supposed that the local crystallization induces the change of the crystal structure of glass-ceramics.Specially,the lattice replacement between Ce³⁺and Ba²⁺ions occurs in the precipitated crystalline phase,thus resulting in the change of the content of Ce3+active centers and the final luminescence properties.The above results provide valuable reference for the preparation of transparent glass-ceramics with high crystallinity and efficient scintillating performance.（3）Eu²⁺-doped transparent glass-ceramics with high crystallinity and regular crystalline domains are prepared by pressureless glass crystallization process.The X-ray induced luminescence intensity of glass-ceramics can be increased by about 20 times compared with that of the as-made glass samples.The scintillating luminescence yield measurement shows that the light output can reach～15000 ph/Me V,which is about 2.46 times higher than that of the commercial BGO crystals.The physical mechanism of the improved scintillating performance is explored.During the heat-treatment under high temperature,the ion substitution between Eu³⁺and Ba²⁺ions occurs in the crystal lattice and the charge compensation effect makes the stable Eu²⁺formed in the glass-ceramics.By this approach,glass-ceramic samples with large size（30 mm in diameter）is prepared.In addition,the samples can also be easily constructed into the form of fiber.By using this glass-ceramic,the radiation detector device is constructed.The test for monitoring gamma ray shows that the maximum error reaches to-11%,which meets the requirement for application as the radiation detectors.Furthermore,an X-ray imaging system is also constructed.The X-ray imaging test shows that the spatial resolution of 12 lp/mm can be achieved.By using an integrated circuit board as the imaging target,X-ray image with high resolution and fine microstructure can be observed.Above results show that the controllable glass crystallization process provides an effective approach for construction of glass-ceramic with high crystallinity,large size,complex shape and optical fiber,thus promising for practical applications in the fields of radiation detection and X-ray imaging.（4）A series of Ba F₂-Ba O-Si O₂ ternary oxyfluoride scintillating glass samples activated with Ce³⁺are designed and successfully prepared.The hybridization modification is expected to change the microstructure and optical response of the materials.Especially,the oxyfluoride glass combines the stability of oxide glass and the lower phonon energy of fluoride glass.The luminescence properties are investigated and the results show that,compared with that of Ba O-Si O₂ oxide glass,the photoluminescence and X-ray induced luminescence intensity of oxyfluoride scintillating glass can be notably improved.The photoluminescence intensity is increased by about 2 times and the X-ray induced luminescence intensity is increased by about3.7 times.The quantum efficiency of oxyfluoride glass is 2 times higher than that of the oxide glass.The physical mechanism of the improved optical properties is studied.The analysis on the valence state of Ce ions shows that the relative content of Ce³⁺in oxyfluoride glass is higher than that in oxide glass.The Monte Carlo simulation is performed to investigated the radiation-matter interaction.It is found that the energy deposition efficiency of X-ray on oxyfluoride glass and oxide glass is similar,which is estimated to be 98.3%and 98.5%,respectively.Above results show that the significant increase of scintillating luminescence is both affected by the energy transfer process between the active dopant and the host,and the luminescence efficiency of Ce³⁺.A prototype device for radiation detection is constructed.The test on the detection performance indicates that the radiation induced luminescence of oxyfluoride glass shows an excellent linear response to the radiation dose.The results demonstrate its promise for practical application for radiation detection.（5）Based on the constructed ternary oxyfluoride scintillating glass,we try to fabricate glass-ceramic samples with high crystallinity.The research purpose is to further improve scintillating performance by control the microstructure of the samples.The crystallization behavior of Ce-doped Ba F₂-Ba₃Si₅O₁₃ glass is studied.It is found that with the increase of Ba F₂content,the crystallization tendency of glass also increases.The crystallization thermodynamics and dynamics analysis indicates that the nucleation rate can be enhanced,leading to the notable decrease in the grain size from more than tens of micron meter to sub-micron meter in the resultant glass-ceramic.The physical mechanism is studied and it is supposed that the addition of Ba F₂ may induce the local phase separation,which is favorable for the heterogeneous nucleation.By optimization of the heat-treatment procedure,the glass-ceramic with high crystallinity and dense crystalline domains is successfully fabricated.The scintillating properties of glass-ceramic are investigated.Compared with the as-made glass,the X-ray induced luminescence of oxyfluoride glass-ceramic is increased by about 2.5 times.Furthermore,the pulse height distribution spectra are measured and the results indicate that the light output of the sample is about 2.7 times higher than that of the oxide glass-ceramic.The scintillating luminescence yield measurement shows that the light output can reach～1416ph/Me V Above results provide a valuable strategy for developing efficient scintillator by regulating the microstructure of glass-ceramics with high crystallinity.