Growth And Physical Properties Of Low Dimensional Hybrid Metal Halide Single Crystals

Hybrid metal halide materials have become one of the most popular materials in the field of optoelectronics and scintillators due to their excellent photophysical properties and low-cost solution preparation.By various connection and extension modes of metal halide polyhedra,hybrid metal halides can form three-dimensional,two-dimensional,one-dimensional,and zero-dimensional structures at the molecular level.The structural diversity of hybrid metal halides endows them with unparalleled diversity and tunability in performance,wherein the diversity of low dimensional hybrid metal halides would by far exceed that of three-dimensional hybrid metal halides without the size limitation of organic ions by the tolerance factor.At the same time,self-trapped excitons（STE）easily form in low dimensional hybrid metal halides due to the quantum confinement and dielectric shielding effects in low dimensional structures,leading to self-trapped exciton emission.Self-trapped exciton emission has the characteristics of broadband emission and low self-absorption,which has important research value in the fields of efficient luminescence,white light emission,and scintillators.In addition,low dimensional hybrid metal halides have great application prospects in the fields of polarized light detection and light modulation on account of their anisotropic performance brought by the intrinsic anisotropy structure.At present,there are still some problems in the development of low dimensional hybrid metal halides,one of which is that the research work on the growth of low dimensional hybrid metal halide single crystals,and thus the structural and physical property study based on these high quality single crystals is still very insufficient.Based on this,we carried out studies in this field and several high-quality single crystals of low dimensional hybrid metal halides have been grown by solution method,and the structure,stability,photophysical properties,anisotropy,and scintillation properties of the materials have been studied in detail.The main content of this thesis is as follows:（1）Centimeter-sized high-quality one-dimensional perovskite（CH₃）₃NHPb I₃single crystals were successfully obtained using an antisolvent vapor assisted method.We have solved the growth cone problem that is prone to occur in the growth of this one-dimensional perovskite single crystal by using iodide additives to regulate the growth of the single crystal.Structural analysis of the single crystal shows that the single crystal contains one-dimensional inorganic chains structure formed by face-shared[Pb I₆]octahedra.However,due to the uneven hydrogen bond interaction between organic ions and the inorganic framework,the symmetry of the inorganic chain has been seriously broken,and the unit cell of the single crystal become very large（c-axis is up to 7.2 nm）.Photophysical testing shows that the band gap of the single crystal is about 3.24 e V.We also found that the single crystal has polarized emission（the degree of polarization up to 0.19）,anisotropic carrier transport（conductivity gap between perpendicular and parallel to the crystal axis up to 22 times）,and a birefringence larger than that of commercially birefringent crystals（0.293@1064 nm）.（2）Centimeter-sized one-dimensional[NH₃（CH₂）₃NH₃]Cu I₃ single crystals with high quality were successfully obtained by solution evaporation method.The crystal structure analysis shows that the single crystal contains one-dimensional chain formed by corner-shared[Cu I₄]tetrahedra.Photophysical testing shows that the single crystal has the band gap of 3.94 e V,the blue light emission characteristic（emission peak position of 438 nm）,and a photoluminescence quantum yields（PLQY）of 26.5%.We investigated the temperature-dependent photoluminescence（PL）and the energy transfer mechanism corresponding to thermal quenching and negative thermal quenching of the single crystal.The X-ray scintillation performance test shows that the light yield of this single crystal is 8100 photons/Me V,and the minimum detection limit is 288 n Gy_air/s.The irradiation stability test found that the irradiation stability of this single crystal is better than that of commercial Cs I:Tl single crystals.At the same time,the relative light output can be renewed to 94.3%from 40%of the fresh one by a low-temperature annealing（at 80°C for 12 h）.（3）A novel zero-dimensional copper（Ⅰ）halide material（N₂H₅）₄Cu₂I₆ with high PLQY and light yield was developed and its centimeter-sized high-quality single crystals were successfully obtained by solution evaporation.The analysis of the single crystal structure shows that in this structure,two[Cu I₄]tetrahedra form the dimer cluster by edge-sharing,and these dimers are isolated by N₂H₅⁺to form a zero-dimensional structure.By adding ethylene glycol,we obtained centimeter-sized high-quality single crystals with regular shape and high transparency.Photophysical property characterization shows that the band gap of（N₂H₅）₄Cu₂I₆ is 3.76 e V,with typical STE emission characteristics.The emission peak position is 525 nm,and the PL lifetime is4.97±0.01μs.The PLQY of（N₂H₅）₄Cu₂I₆ single crystals up to 91%.We investigated the temperature-dependent PL and the energy transfer mechanism corresponding to thermal quenching and negative thermal quenching of the single crystal.The X-ray scintillation performance test of（N₂H₅）₄Cu₂I₆ single crystal shows that the light yield reached 40400 photons/Me V,and the linear response test shows that it has a good linear response to the dose rate of X-ray in the dose rate range of 1.7-18 m Gy_air/s.