Synthesis And Luminescence Properties Of Zero-dimensional Organic Metal Halides

Organic metal halides have attracted great interest and been widely used in many fields such as solar cells,photodetectors,light-emitting diodes.In addition,the organic metal halides have various structures and compositions,which endow them with rich physical properties.In this dissertation we review the important roles of the organic molecules in determining the structure and properties of the organic metal halides.Based on these,a series of novel zero-dimensional organic metal halides were synthesized by hybridizing several kinds of organic molecules with the copper halides or tin halides.The structure-property relationship of these zero-dimensional organic metal halides was investigated by using the experimental studies and first principles calculations.The major research contents are as follows:(1)The zero-dimensional organic metal halide with wide luminescence band,large Stokes shift,and long lifetime was synthesized.The experiments and calculations show that the luminescence stems from the self-trapped excitons.The high-frequency phonons provided by the organic cations promote the long-lifetime luminescence of these crystals,and the low-frequency optical phonons provided by the polyhedra account for the broadening of the luminescence.The excitation and emission photon energies of the triplet states of such crystals were calculated by using the density functional theory method,and the results match well the experimental results.The self-trapping of the excitons and the intersystem crossing together account for the large Stokes shift.(2)Three kinds of novel zero-dimensional organic metal halides were synthesized and their photoelectric properties were investigated.These crystals contain the same type of organic cation and have similar preparation methods,but they contain different types of polyhedra.Their stable phases are composed of octahedra for the bromide and iodide but disphenoids for the chloride.The experiments show that the halides have the largest Stokes shift.In addition,the chloride shows monoexponential luminescence decay,while the bromide and iodide show biexponential luminescence decay.The results reveal that the constructing polyhedral unit with smaller coordination number has a larger Stokes shift and stronger electron–phonon coupling.In addition,the crystal composed of the polyhedral units with a smaller coordination number has nearly degenerate lowest unoccupied electronic bands,while the crystal composed of the polyhedral units with a bigger coordination number exhibits the degeneracy lift of the lowest unoccupied electronic bands.These findings improve our understanding of the role of the polyhedron type in the photodynamic of the zero-dimensional organic metal halide.(3)The photodynamics of the six novel types of low-dimensional hybrid copper halides was investigated.The experiments in conjunction with the density functional theory calculations indicate that these copper halides exhibit two kinds of self-trapped excitons with different electron-phonon coupling strengths,temperature dependence,and lifetimes.These two kinds of excitons belong to one-scenter and two-center self-trapped excitons,respectively.The large hole effective mass and low-dimensional structure of these copper halides promote the formation of the one-scenter self-trapped excitons,and the softer organic cations in the lattice lead to stronger local deformation which is favorable for the formation of the two-center excitons.There is phase transition between the one-center and two-center self-trapped excitons at the elevated temperatures.