Synthetic Methods And Luminescence Properties Of Novel Multicomponent Metal Halides

Photoluminescence is the phenomenon in which a material emits light when excited by absorbing light of a specific wavelength（ultraviolet,visible or infrared）.The mechanism is that when the material exposed under ultraviolet light,their outer electrons transit to the excited state of the unstable state,and then they will return to the ground state,and the energy is released in the form of light in this process.Such materials called photoluminescent materials.Photoluminescent material has great potential in carrying information and has an ability to convert specific signals.Among them,multicomponent metal halides represented by traditional three-dimensional（3D）lead halide perovskite materials Cs Pb X₃（X=Cl,Br,I）have shown extremely high potential application value in the field of studying luminescent materials and designing device.Therefore,it has become an important topic to develop novel multicomponent metal halide luminescent materials,find amazing optical properties（such as realizing the regulation of their different luminescent colors）,and study their luminescent mechanism.Besides,single crystal materials can be easily used to study the luminescence mechanism,and their stability is also pretty good.And all these reasons make luminescenct single crystals become a very ideal research object.Based on these,several multicomponent metal halide single crystals were shown in this thesis,and their structures and corresponding luminescence or color-changing properties were studied in detail,respectively.The main contents and inovations are as follows:（1）A ternary all-inorganic cadmium halide single crystal Cs₇Cd₃Br₁₃ was designed and synthesized.In its single crystal structure,a 4-coordinated isolated[Cd Br₄]^2-and a corner-sharing 6-coordinated[Cd Br₆]^4-one-dimension chain coexistence.The special crystal structure makes the needle-like single crystals have orange luminescence at 630 nm when excited by ultraviolet light.Temperature-variable spectroscopy with theoretical calculations explain that the emission of the single crystal originates from the self-trapped exciton emission of the two polyhedra.Besides,all-inorganic polyvalent cadmium halide luminescent single crystals are rare.（2）A series of single crystals Cs₄Pb Cl₆:Mⁿ⁺doped with different valences of metal ions(Mⁿ⁺:Zr⁴⁺/Sn²⁺/Sb³⁺/Mn²⁺)were designed and synthesized here.The luminescence properties of the doped host are changed by doping.Cs₄Pb Cl₆ has no emission in the visible light region,and the emission of the doped single crystal covers the full visible light region（blue,green,yellow and red）.Variation-temperature spectroscopy demonstrates that these luminescent single crystals employ two different emission mechanisms.After excitation,the Mn-doped sample undergoes a"free exciton-Mn²⁺"energy transfer process generated by the host lead halide polyhedron,and then a spin-forbidden ⁴T_1g→⁶A_1g transition of Mn²⁺occurs.The other three doped single crystals have self-trapped exciton（STE）emission with dopants.Sb³⁺and Sn²⁺are both emitters and sensitizers.In addition,the dopant ratio in Cs₄Pb Cl₆ was successfully tuned by two different methods（hydrothermal synthesis and precipitation synthesis）.（3）An organic-inorganic hybrid Cu（I）halide single crystal Py Cs₃Cu₂Br₆（Py:pyridinium）was designed and synthesized,in which pyridine and cesium ions coexisted as balance cations together.The incorporation of organic pyridines changes the symmetry of the single crystal and changes the coordination environment of Cu（I）.Particularly,Cu（I）tri-coordinates with bromine atoms to form a zero-dimensional planar triangular structure.Py Cs₃Cu₂Br₆ exhibits a hexagonal channel structure which help it to respond to external stimulations such as mechanical force,heat,mositure,and amine vapor.This structure provides a channel for active molecules to diffuse and interact with the pyridinium,resulting in a stimulus-triggered decomposition into Cs₃Cu₂Br₅ with high blue light emission.