Synthesis, Crystal Structure And Photoluminescence Properties Of Low-dimensional Lead-based Halides

In recent years,low dimensional lead halides have attracted wide attention in the fields of light-emitting diodes and solar cells due to their flexible structure,simple preparation process,high carrier mobility and high photoluminescence quantum efficiencies(PLQEs),Among them,it has an important application in the preparation of white light emitting diodes(WLED).In this paper,guided by the structure directing effect of organic cations,we selected different kinds of organic amines as cations,lead chloride or lead bromide as optical active centers to synthesize low dimensional organic-inorganic hybrid lead halide functional materials.The research contents and achievements are summarized as follows:(1)Based on different kinds of organic cations as structural modification strategies,we synthesized two kinds of 0D hybrid lead bromide compounds,namely as,[Me BAPIm]₂Pb₃Br₁₂(1)([Me BAPIm]=2-methyl-1,3-bis(3-aminopropyl)imidazolidine)and[PMDPTA]₂Pb₃Br₁₂(2)(PMDPTA=pentamethyldipropene triamine)via facile solvothermal reaction.Both compounds contain[Pb₃Br₁₂]^6-trimers based on face-shared[PbBr₆]octahedrons.Upon UV light excitation,compound 1displays broadband yellow emission covering entire visible spectra with PLQE of4.57%.The broadband light emission can be ascribed to the self-trapped excitons based on systematical characterizations including steady-state,temperature-dependent and time-resolved emission spectra,and so forth.The white light emitting device can also be easily fabricated by coating the sample of compound 1 on a blue light emitting diode.(2)By using an optically active 1,3-bis(4-pyridyl)-propane(BPP)as organic cation,we successfully assembled two new hybrid lead halides of[H₂BPP]Pb₂X₆(X=Br:3 and Cl:4)containing one-dimensional double[Pb₂X₆]^2-chains.Under UV light excitation,compounds 3 and 4 exhibit broadband yellowish-green emissions verified by promising photoluminescence quantum efficiencies(PLQEs)of 8.10%and 4.84%,respectively.The broadband light emissions derive from the combination of dual higher-energy blue and lower-energy yellow light spectra,which can be attributed to the individual contributions of organic and inorganic components,respectively,according to the time-resolved and temperature-dependent emission spectra as well as theoretical calculations.This work proves the great contribution of organic components for the photophysical properties and provides a new design strategy to realize broadband light emission by rationally combine the dual-emitting properties of different assembly blocks.(3)By selecting different kinds of organic cations as templates,we synthesized three new one-dimensional(1D)lead halides,[(Me)₄-pipz]PbCl₄(5),[(Me)₄-pipz]PbBr₄(6)and[DAPr-pipz]PbCl₄·H₂O(7),connected by purely corner-shared tetragonal pyramid building units of PbX₅(X=Cl,Br).The inorganic parts of all three compounds contain 1D[PbX₄]^2-chains connected by purely corner sharing building units of PbX₅(X=Cl,Br)tetragonal pyramids.Among them,compound 7 exhibits broadband yellow-green emission with photoluminescence quantum efficiency(PLQE)of 1.64%excited by UV light.This work provides a novel structural model to understand the relationship between structure and photoluminescence.