Structure And Function Design Of Metal Halide Scintillator And Its Application In X-ray Imaging

X-ray detection plays an extremely important role in medical diagnosis,nondestructive testing,safety testing,scientific research,environmental monitoring and other practical applications.At present,the research focus is mainly on traditional inorganic semiconductors,such as amorphous selenium,crystalline silicon and pure germanium.However,the preparation of these typical X-ray detection materials or devices usually requires high-temperature or high-vacuum environments and complex manufacturing processes.In addition,the X-ray doses currently used in imaging equipment are large and pose a significant safety risk to human health.Considering these defects,it is of great research significance to develop a new generation of highly sensitive and stable X-ray detectors so as to reduce the harm caused to human health by the use of X-rays.Metal halide materials with high X-ray attenuation coefficient,tunable band gap and large carrier migration lifetime（μτ）product have proved to be promising X-ray detection materials,which can solve the shortcomings of traditional X-ray detectors.X-ray detectors are divided into indirect X-ray detectors and direct X-ray detectors according to the working principle.At present,indirect X-ray detectors based on scintillator materials are widely used and have the potential to combine with mature sensor arrays for dynamic scanning detection and diagnosis,and have been widely used in ordinary flat X-ray detectors.Among the various properties of scintillator materials,the light yield is one of the parameters most closely related to the detector efficiency and resolution.The luminescence performance of the scintillator has a direct impact on the X-ray imaging effect.The relationship between the structure and luminescence properties of metal halide scintillator materials reported at present is still in the initial stage.How to adjust the luminescence properties of the scintillator by adjusting the structure of the metal halide needs further investigation.In addition,most of the metal halide scintillators are rigid films with poor mechanical properties,which will inevitably produce vignetting problems when X-ray imaging curved objects,resulting in reduced imaging resolution.What’s more,rigid scintillator films are also not resistant to bending and lose their use value once damaged.In addition,most metal halide scintillators also have a long afterglow effect,requiring a longer exposure time to obtain a clear image,which is not conducive to the realization of fast dynamic X-ray imaging.Therefore,it is urgent to design some new metal halide scintillators to effectively solve the above problems.In this thesis,the structure,properties and imaging applications of the metal halide scintillator materials are designed and studied.In terms of structure,solvent molecules were designed to participate in the crystal structure of the metal halide scintillator,and the conformation arrangement of organic cations at the A-site was regulated by constructing different intermolecular forces,so as to explore the relationship between metal halide structure and luminous properties,and further realize large-area X-ray imaging.In terms of performance,in order to further expand the application range of metal halide scintillator,an intermolecular force was designed to embed the metal halide scintillator into the organic gel to give it flexible super stretching and self-healing properties,so as to achieve curved X-ray imaging,stretchable X-ray imaging and self-healing X-ray imaging in water,providing ideas for the future design of multi-functional wearable anti-radiation clothing.In imaging applications,direct metal halide semiconductor materials and indirect scintillator materials are combined to design energy transfer strategies,so as to shorten the response speed of the metal halide scintillator and avoid long afterglow effect to achieve fast X-ray imaging,which points out the direction for the design and research of new metal halide X-ray detectors.The main research contents of this paper are as follows:In the second chapter,we study the co-assembly strategy of solvent molecules and metal halide scintillator ions and successfully prepare two zero-dimensional（0D）scintillator structures by constructing intermolecular forces.The solvent molecules H2O and CH₃CN form hydrogen bonds with the amino（-NH₂）and carboxyl（-COOH）groups of the A-site organic cations,respectively,which results in the different molecular conformations of the A-site organic cations in the two 0D crystal structures.Compared with（DABA）2Mn Br4?CH3CN crystal,（DABA）2Mn Br4?H2O crystal has stronger supramolecular force,which enhances the rigidity of the crystal structure and thus effectively inhibits non-radiative transitions,resulting in a higher photoluminescence quantum yield.The photoluminescence quantum yield is 25 times higher than（DABA）2Mn Br4?CH3CN crystal.In addition,in the natural environment without any packaging,the two solvents co-assembled single crystals showed good stability,and fluorescence intensity remained unchanged for more than one month.The large-area（DABA）2Mn Br4?H2O scintillator also has potential applications in hard X-ray imaging with spatial resolution up to 5.0 lp mm^-1.The solvent co-assembly strategy provides a new approach for the design of high luminescent metal halide scintillators.Although metal halide scintillator materials with high photoluminescence quantum yields have absolute advantages in X-ray imaging,the rigid scintillator films currently prepared will cause the phenomenon of the vigil of curved objects during imaging,requiring multiple X-ray exposures to obtain clear images,which is not good for human health.In addition,the rigid scintillator film is not resistant to bending and has poor mechanical properties,which reduces the service life.In order to further expand the practical application of metal halide scintillator,a novel 0D（C38H34P2）Mn Br4 scintillator/organogel composite material was prepared in the third chapter.Since the coordination bond formed by manganese ion in（C38H34P2）Mn Br4scintillator and carbonyl group in organic gel can be used as a physical crosslinking point,the（C38H34P2）Mn Br4 scintillator/organogel composite can effectively dissipate energy during the tensile deformation process,thus improving the tensile property,and its elongation can reach 1300%.As a result,it can achieve X-ray imaging in the range of 0-500%reversible stretching,and the circuit structure inside its electronic components is still clear during the stretching process.In addition to coordination bonds,hydrogen bonds also exist in the（C38H34P2）Mn Br4 scintillator/organogel composite,and these two forces make it self-healing properties.In traditional projection X-ray imaging,the imaging resolution can reach 14.0 lp mm^-1.It can also be molded into various shapes and attached to curved objects for X-ray imaging to solve the problem of vignetting curved objects by rigid scintillators during X-ray imaging.In addition,the（C38H34P2）Mn Br4 scintillator/organogel composite can also achieve X-ray imaging in the range of-196 ^oC-200 ^oC,which has the potential to be applied to high-temperature X-ray imaging.In addition,because the organogel plays a protective role for（C38H34P2）Mn Br4 scintillator,it still has good humidity stability under the condition of70-80%humidity and can realize curved and self-healing X-ray imaging in water,which provides good design idea for the future design of new multi-functional wearable anti-radiation clothing.In the fourth chapter,in order to solve the problem of a long average lifetime and afterglow effect of most metal halide scintillators,we design a new direct-indirect hybrid X-ray detector,which combines the direct metal halide semiconductor material3D MAPb I3 with the indirect metal halide scintillator material 0D Cs3Cu2I5 through a low-cost and rapid pressing process.Due to the rapid energy transfer from Cs3Cu2I5 to MAPb I3,the X-ray response time of the hybrid device is greatly reduced by nearly 30times to 36.6ns.In addition,Cs3Cu2I5 exists at the grain boundary of MAPb I3 crystal,which blocks the ion migration path of the device,thus reducing the noise and dark current of the device.After storage without any packaging for about one month,the hybrid device responds stably to hard X-ray pulses with no signal/noise ratio loss.Finally,we demonstrate the rapid imaging capability of the hybrid device by taking the pen tip as the imaging target,which provides the research basis for the realization of dynamic X-ray imaging in the future.This new kind of X-ray detector provides strong competitiveness by combining the advantages of both direct semiconductors and indirect scintillators for next-generation products.In summary,the structure,properties and imaging application of metal halide scintillators are studied in this thesis.The relationship between the structure and luminescence of metal halide scintillator was investigated by designing intermolecular forces.In terms of performance,the metal halide scintillator is evenly embedded in the organic gel through the design of intermolecular force,so that it has super stretching and self-healing properties,and can achieve curved,stretchable and self-healing X-ray imaging in water,which provides research idea for the design of radiation-resistant wearable clothing in the future.In imaging applications,the design of direct/indirect hybrid X-ray detectors improves the response speed of hybrid devices,avoids the afterglow effect of metal halide scintillators and the problem of optical signal crosstalk,solves the ion migration problem of semiconductor materials,and provides a valuable reference for fast X-ray imaging.