Non-lead Halide Scintillators: Characterization,Arrayed-Structure Preparation And X-ray Indirect Detection

Currently,X-ray detection has penetrated into all aspects of human activities,ranging from security inspection,nondestructive testing,medical imaging,astronomic observation,national-defense military to study of high energy physics.In order to improve the detection capability,the development of its core component scintillator is particularly important.Recently,lead halide perovskites(such as Cs Pb X₃)have attracted wide attention in the scintillator field due to the advantages of low cost,facile preparation,heavy element composition,high luminescence efficiency.However,the physiological toxicity and environmental pollution of lead are criticized.In order to inherit the advantages of halide perovskite scintillators and avoid lead toxicity,it is of great significance to develop new non-lead halide scintillators.In addition,the scattering of photons in the scintillator layer has a harmful impact on the quality of X-ray imaging,however,this has not been explored in revelant studies.Based on this,my dissertation focuses on the exploration of new non-lead halide scintillators.I have developed a series of transition-metal halides,which enjoy weak self-absorption,efficient luminescence,low cost and facile preparation.I have also systematically studied their relevant luminescent properties and scintillator performance.Scintillator films with column arrayed structure have been prepared which showed suppressed light scattering and resulted in higher spatial resolution during X-ray imaging.My work reveals the potential of new lead-free halides in the field of scintillator applications.The main contents of this dissertation are as follows:(1)(C₆H₅CH₂CH₂NH₃)₂MnBr₄(PEA₂MnBr₄)single crystal was firstly prepared,then its crystal structure and properties were analyzed and systematically studied.Spectroscopic characterization found that it has a narrow band gap of 1.65 e V,emits green light at 530 nm(due to the ⁴T₁(G)?⁶A₁ transition of Mn²⁺)with?s lifetime and decent photoluminescence quantum efficiency.Subsequently,X-ray fluorescence,X-ray absorption coefficient,effective atomic number and light yield level(13.58%of Lu_1.8Y_0.2Si O₅:Ce(LYSO))of PEA₂MnBr₄ were evaluated,confirming its research potential in scintillator.(2)In order to avoid the low stability from hybrid structure and self-absorption caused by ion luminescence,K₂Cu X₃(X=Cl,Br)with all-inorganic structure,weak self-absorption and highly efficient luminescence were further developed,their structure,luminescence and scintillator properties were studied systematically.Theoretical calculations showed that their one-dimensional crystal structure renders to their low electronic dimensionality and strong electron-phonon coupling.Spectroscopic characterization showed that the lattice was very soft,and the self-trapped exciton was easily generated under strong electron-phonon coupling,thereby exhibiting a large Stokes shift(102 nm).The weak self-absorption and high photoluminescence quantum efficiency(98.77%)benefited a good light yield.The light yields of K₂CuCl₃ and K₂Cu Br₃ were74.62%and 81.49%of LYSO,and the lowest detection limit was 172.8 n Gy_air·s^-1 and132.8 n Gy_air·s^-1,respectively.All-inorganic structure confirmed the excellent structure and luminescence stability.(3)X-ray imaging with K₂CuCl₃scintillator was further performed.To suppress photon scattering inside scintillator,K₂CuCl₃ columnar arrays were prepared by hot pressing method with AAO porous template.The X-ray imaging results showed that the imaging quality using K₂CuCl₃ columnar arrays was significantly better than that of Gd₂O₂S:Tb³⁺(GOS)with high light yield.Thanks to spatial confinement of AAO,the columnar arrays served as waveguide and the photon scattering was effectively suppressed,finally improved the spatial resolution of imaging.(4)In order to completely avoid the radiation background problem and further improve the X-ray absorption capacity,scintillator performance of Cs₃Cu₂I₅,which was the heavier analog of K₂CuCl₃ and exhibited no radiation background,was further studied.Cs₃Cu₂I₅ with zero-dimensional structure exhibited a soft lattice(Huang-Rhys factor is46.69),which also shows an efficient self-trapped exciton luminescence.Furthermore,its highly matching blue emission,short life time and larger Stokes shift have more advantages for scintillator applications.The X-ray absorption capacity of Cs₃Cu₂I₅ was equivalent to LYSO and Cs I:Tl(Cs I),and its light yield was 31,694 photons·Me V^-1.The linear dynamic range spaned five orders of magnitude,and the lowest detection limit reached 24.33 n Gy_air·s^-1,showing excellent scintillator performance.Cs₃Cu₂I₅ columnar films were subsequently prepared by hot-pressing method for X-ray imaging.Imaging results showed that its light yield was slightly inferior to that of Cs₃Cu₂I₅ polycrystalline film and GOS,but its spatial resolution was obviously better(Cs₃Cu₂I₅ columnar arrays,its polycrystalline film and GOS:5.4 lp·mm^-1,4.3 lp·mm^-1 and 3.9 lp·mm^-1,respectively).