Synthesis And Luminescence Mechanism Of Diamine Organicinorganic Hybrid Metal Halide Materials

Organic-inorganic hybrid metal halides generally have a perovskite-like(ABX3)structure.In recent years,due to its superior photoelectric performance and various composition or structure tunability in light emitting diode,photovoltaic,ferroelectric,photoelectric detection,display,laser and other fields have attracted great attention.In this paper,a series of lowdimensional organic-inorganic hybrid metal halides were assembled by several simple methods,using trans-2,5-dimethylpiperazine(TDMP)diamine organic molecules as organic cations and a variety of metal cations(Pb,Cd,Mn,Sb)as emission centers and inorganic ion skeletons.The crystal structure,chemical composition,lattice vibration and optical properties of these solid compounds were investigated by a series of different characterization methods.In addition,the electron band structure and density of states(DOS)are calculated by density functional theory(DFT),which can be used to further analyze and understand the optical properties and emission mechanism of these compounds.The research contents and results are as follows:(1)A series of(TDMP)Pb Br4 and Mn doped(TDMP)Pb Br4 powder crystals with high water resistance were synthesized by the hydrothermal method,TDMP is a diamine molecule and Pb Brx clusters exist in pairs.The optical properties and detailed optical physical processes are systematically studied experimentally and theoretically(absorption,luminescence of different excitations,temperature-dependent luminescence,luminescence dynamics,Raman spectroscopy,etc.).The results show that diamine molecules can couple adjacent bound excitons and enhance the anharmonic electron-phonon coupling of the system.The addition of adjacent manganese ions will introduce spin-spin ferromagnetic coupling,further enhance the electric phonon coupling,and produce magnetic bipolaron states.In addition,the absorption quenching between luminescent centers can be reduced by regulating the spacing of adjacent magnetic bipolarons by doping concentration.Experiments prove that the system in the initial doping concentration is approximately 20%,PLQY can reach to 92.5%,particularly efficient red emission performance,in addition the sample under room temperature or low laser power can emit strong red emission,when temperature is low or laser power is bigger,because the electron phonon coupling decreases or carrier repulsion increases,can also be issued a green emission.The LED light prepared by this method shows good stability.This series of materials is of great significance to understand the applications of magnetopolarons in material design,lighting physics,display,tuned luminescence,temperature sensing,waterproof material field,spin luminescence and so on.(2)(TDMP)Mn Br4 single crystal was synthesized by a solvent slow evaporation method,in which Mn Brx clusters existed independently to form zero-dimensional domain structure.Yellow-green luminescent(TDMP)Mn Br4 SCs were obtained,in which the nearest manganese ion spacing was 6.8 (?) and PLQY up to 89%.Compared with the previous manganebromine single crystal constructed by diamines with manganese ion spacing of 6.6 (?),this ion spacing is the critical distance to block spin-spin coupling,or the distance between spin polarons,within which polaron molecules or magnetic bipolarons can be formed,and beyond which monopolarons can be formed.In this system,two Mn2+ and diamine organic molecules are beneficial to the formation of bipolaron through cooperative electric-phonon coupling,which also strongly depends on the separation of Mn-Mn.Interestingly,charge transfer,d-d transition,strong electron-phonon coupling and magnetic coupling are all involved in their optical processes,which results in a unique nonlinear optical phenomenon for some transitions excited by continuous lasers.Single crystal exhibits different emission colors under different laser excitation wavelengths due to the different contributions of different transitions.This finding is helpful to guide the design and regulation of manganese based luminescent materials in the future.The LED light prepared by this method shows good stability.(3)(TDMP)Sb Cl5,(TDMP)Cd Cl4,and Sb doped(TDMP)Cd Cl4 were synthesized by slow cooling method.It was found that effective trilinear luminescence could be produced by embedding diamine molecules into antimony chloride lattices,but concentration quenching between the luminescence centers still existed.By doping appropriate amount of Sb3+ into TDMP embedded cadmium chloride one-dimensional domain limited lattice,the concentration quenching of Sb3+ luminescence center can be effectively inhibited,and highly efficient selfbound state luminescence materials can be obtained.(TDMP)Sb Cl5 single crystal exhibits yellow emission under ultraviolet excitation,and photoluminescence efficiency is 27%;(TDMP)Cd Cl4 shows weak blue emission;The luminescence efficiency of Sb3+ doped(TDMP)Cd Cl4 exhibits yellow emission under ultraviolet excitation is 99%.The electron band structure calculated by density Functional theory(DFT)shows that Sb3+ doping regulates the red shift of(TDMP)Cd Cl4.Raman spectroscopy proves that TDMP is embedded in the lattice structure of the multi-phonon scattering mode,and the variable temperature luminescence spectrum reflects the strong electron-phonon coupling,which provides support for the strong inter-system channelhopping and S-T internal conversion,leading to the efficient luminescence of the doped system.