Luminescent Characteristics And Applications Of Copper Halides With Zero-Dimensional Crystal Structures

Luminescent materials have been widely used in lighting and display,medical imaging,non-destructive testing,information security,etc.In recent years,three-dimensional（3D）lead-based halide perovskites represented by conventional Cs Pb X₃（X=Cl^-,Br^-,I^-）have been widely used in light-emitting diodes（LEDs）,solar cells,scintillator and other fields due to their excellent optoelectronic properties.However,the poor stability and the toxicity of lead in 3D lead-based halide perovskites have seriously restricted their commercialization.Therefore,a wide range of researchers are working on structural design and dimensional modulation based on 3D metal halides,and trying to explore other metal halides with excellent properties,a large family of metal halides has been formed as a result.Compared with the traditional 3D and low-dimensional metal halides,the zero-dimensional（0D）metal halides,which are relatively less toxic,stable,with a wide variety of structural units and diverse optical properties,have a broader application prospect.Based on this,this thesis focuses on 0D copper halides,firstly,the self-trapped excitons（STEs）luminescence mechanism of the 0D Cs₃Cu₂X₅was deeply studied,then a series of highly luminescent 0D hybrid copper halides were developed,their structures,optical properties and application fields were systematically investigated.Finally,a series of new copper halides were designed and synthesized with the guidance of the structure-luminescence relationships of the 0D hybrid systems.Relying on the rich structural and photophysical properties,0D copper halides show great development potential.The main results are as follows:（1）Study of luminescent properties of Cs₃Cu₂X₅ and emission mechanism of STEs.The0D Cs₃Cu₂X₅ phosphors were synthesized by hot injection method,and a series of physical characterizations revealed that Cs₃Cu₂X₅ systems have high phase purity and the copper elements in the samples are in the form of Cu⁺.Among them,Cs₃Cu₂Cl₅ phosphor emits green light,the photoluminescence quantum efficiency（PLQE）is as high as 91.3%,and the photoluminescence decay lifetime up to 112.4μs.The photophysical characterization revealed that the photoluminescence decay lifetime of Cs₃Cu₂Cl₅ is extremely sensitive to the temperature,with a high sensitivity of up to 3081 ns/℃.Using Cs₃Cu₂Cl₅ as the research object,the transient absorption test directly proved the emission mechanism of Cs₃Cu₂Cl₅ is STEs emission with a generation time of about 330 fs.Finally,the lattice structure distortion of Cs₃Cu₂Cl₅ in the excited state was deeply studied by theoretical calculations,i.e.,the asymmetric[Cu₂Cl₅]^3-edge-shared dimer in the ground state changed to the symmetry-enhanced[Cu₂Cl₅]^3-coplanar dimer in the excited state.While the photogenerated STEs were confined within the[Cu₂Cl₅]^3-coplanar dimer with a strong quantum confinement effect,so that Cs₃Cu₂Cl₅ exhibited efficient luminescence performance.（2）Study on the optical properties and applications of multiple metal halide configurations of hybrid copper halides.Considering the structural tunability and diverse optical properties of 0D copper halides,three different types of A-site organic cations were introduced to successfully synthesized three different metal halide configurations of 0D hybrid copper halides,and their structures,optical properties and application fields were systematically investigated.Specifically,（a）blue-and green-emitting single crystals of（TBA）Cu X₂(TBA=C₁₆H₃₆N⁺,X=Cl^-,Br^-),are composed of[Cu X₂]^-rod-like monomer configurations as structural units,and the luminescence mechanism is STEs emission,flexible scintillation screens prepared using（TBA）Cu X₂ have certain application advantages in the field of flexible X-ray imaging.（b）Dual-band white light-emitting single-crystalline（TPA）₂Cu₂I₄(TPA=C₁₂H₂₈N⁺)is composed of[Cu₂I₄]^2-dimers,which is a rare single-component white light-emitting material with both high PLQE of 84.4%and high color rendering index of 91,and the luminescence mechanism is derived from the dual STEs emission.The UV-pumped white light LEDs prepared by using（TPA）₂Cu₂I₄ can be used to solid-state lighting field.（c）The yellow-emitting single crystals of（PTMA）₃Cu₃I₆(PTMA=C₉H₁₄N⁺)is composed of[Cu₃I₆]^3-trimers,and its yellow light emission is originated from the radiative recombination of electrons in the conduction band minimum of organic molecule PTMA⁺with holes in the valence band maximum of the[Cu₃I₆]^3-trimer through intersystem crossing.In addition,the（PTMA）₃Cu₃I₆ single crystals also exhibited low-loss optical waveguide and highly polarized emission.（3）Design synthesis and application study of dimer and trimer configurations of hybrid copper halides.New copper halides were successfully designed and synthesized using the above-mentioned structure-luminescence relationships of 0D hybrid copper halides as a guide.Specifically,（a）（ETPA）₂Cu₂I₄(ETPA=C₁₁H₂₆N⁺)single crystals were prepared with the guidance of the structure-luminescence relationships of the（TPA）₂Cu₂I₄,exhibiting two distinct isomers.Two different space groups of（ETPA）₂Cu₂I₄ single crystals under 365 nm UV excitation,one emitted white light and the other emitted blue light.The blue-emitting（ETPA）₂Cu₂I₄ single crystals also exhibit thermochromic luminescence,and emited warm white light at high temperature.（b）Still guided by the structure-luminescence relationships of the（TPA）₂Cu₂I₄,Cu-Ag co-occupied（TPA）₂Cu Ag I₄ single crystals were prepared by introducing Ag atoms at the B-site,which exhibited triple exciton ultra-broadband warm white light emission properties.（c）Finally,the yellow-emitting single crystals of（BTMA）₃Cu₃I₆(BTMA=C₁₀H₁₆N⁺),which was prepared with the guidance of structure-luminescence relationships of the（PTMA）₃Cu₃I₆,is composed of three tetrahedrons connected by coplanar connection to form[Cu₃I₆]^3-trimers,and its yellow emission mechanism is consistent with that of（PTMA）₃Cu₃I₆.（BTMA）₃Cu₃I₆ 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