Synthesis And Broadband Emission Properties Of One-dimensional Organic-inorganic Hybrid Metal Halides

Organic-inorganic hybrid metal halide materials possess the outstanding structural tuneability and excellent photoelectric properties,which therefore shows the great potential applications in many fields,such as photovoltaics,lasers,light-emitting diodes and photodetectors.Compared with three-and two-dimensional structures,one-dimensional metal halides have unique quantum wire structures,more localized electronic states,much wider band gap,and larger exciton binding energy,thereby exhibiting the excellent broadband emission properties,e.g.high quantum yield(?60%)and long fluorescence lifetime.However,there is still a lack of effective design strategies to improve and regulate the broadband emissions in the one-dimensional systems.Therefore,it is of great importance to develop the new high-efficiency one-dimensional hybrid metal halide-based photoluminescent materials and investigate the origin of the broadband emissions.Based on the function-oriented structural design concept,this thesis focuses on one-dimensional hybrid metal halides,Pb²⁺and Sb³⁺ions with ns² electronic configuration and transition metal ions Cd²⁺are selected as the optical active centers,and regulates the structures of organic amine cations and the types of halogen ions to design and synthesize a series of new one-dimensional organic-inorganic hybrid metal halides with broadband emission properties.The main studies in this thesis contain the following two aspects:1.In order to enrich the structural family of one-dimensional pure face-shared perovskite-like metal halides and further optimize their broadband emission performances,for instance quantum yield,we have prepared three new one-dimensional hybrid metal halides by the solution volatilization,namely,(2cepi H)Cd Cl₃(1),(2cepi H)Pb Br₃(2),and(2cepy H)Pb I₃(3)(2cepi=1-(2-Chloroethyl)piperidine,2cepy=1-(2-Chloroethyl)pyrrolidine).The crystal structures of 1-3 contain one-dimensional polyanionic chains by face-sharing the MX₆octahedra(M is metal,X is halogen).1 shows excellent broadband white light emission,such as ultra-high color rendering index(89).To our knowledge,it is for the first time that the broadband emissions based on self-trapped excitons are observed in one-dimensional Cd-based metal halides.Both 2 and 3 exhibit broadband yellow light emission properties.2 has a quantum yield of 16.8%,exceeding all reported one-dimensional pure face-shared metal halides.Variable temperature photoluminescence spectra proves that the broadband white light emission of 1originates from the synergistic emissions of free excitons and self-trapped excitons,and those of both 2 and 3 stem from the radiative recombination of exciton states self-trapped into the highly distorted octahedral lattice.In addition,1-3 show the potential semiconductor properties.This work provides an important theoretical guidance for the synthesis of novel single-component high-efficiency broadband emissive materials.2.Taking into advantages of the stereochemical activity of the lone pair of electrons(5s²)to construct the MX₅ square pyramid structure unit in the molecular system,two isostructural antimony-based metal halides,namely(2cepy H)Sb Cl₄(4)and(2cepy H)Sb Br₄(5),were synthesized.Both compounds contain a one-dimensional polar polyanionic chain formed by corner-sharing Sb X₅ square pyramid units.It is shown that the optical and photophysical properties and electronic band structure of compounds are susceptible to the nature of halogen ions.4 exhibits the broadband yellow light emission derived from triplet excitons(phosphorescence),as proved by its long lifetime and temperature dependence of broadband emission.To our knowledge,this is the first report that broadband emission properties are discovered in one-dimensional antimony-based hybrid metal halide constructed by MX₅ square pyramid units.The introduction of the heavier Br atom leads to the fluorescence quenching of5.Moreover,5 shows more excellent nonlinear optical properties(3.2×KDP)than 4(1.8×KDP).The bandgap of 4(3.33 e V)is larger than that of 5(2.82 e V).This work opens up a new way for constructing polar broadband emission materials with novel structures.