Luminescent Properties Of Zero-Dimensional Lead-Free Organic-Inorganic Hybrid Metal Halides

Organic-inorganic hybrid metal halides have become a hot topic in the research of photofunctional materials and devices,and their luminescence properties can be modulated by designing different crystal dimensionalities,changing organic/inorganic components,and doping ions.Given the toxicity of Pb and the instability of the three-dimensional structure,the application of threedimensional Pb-based conventional chalcogenide materials is limited.Therefore,the study of the design and preparation,photochromic modulation and structurephysical relationship of low-dimensional,lead-free metal halide light-emitting materials is important for the expansion of such materials in the field of solid-state lighting and display.The present study focuses on several novel zero-dimensional lead-free metal halide light-emitting materials,including:1)New lead-free zero-dimensional(0D)(C7H8N3)3InX6·H2O(X=Cl,Br)single crystals were synthesized,which shows broad yellow emission due to selftrapped excitons(STEs).First-principles calculations indicates valance band maximum is partially made of π orbitals from[C7H8N3]+.(C7H8N3)3InX6·H2O show indirect optical gap,which may be resulted from this organiccontributed band edge.Despite the indirect-gap nature with extra phonon process during absorption,the photoluminescence(PL)of(C7H8N3)3InBr6·H2O can still be significantly enhanced through Sb doping,with the photoluminescence quantum yield(PLQY)increased tenfold from 5%to 52%.2)A new 0D In-based OIMH(C11H24N2)2[InBr6][InBr4]with high-efficiency red PL was synthesized.This compound is composed of two different inorganic units[InBr6]3-octahedra and[InBr4]-tetrahedra which are separated by organic(C11H24N2)2+cations.The titled compound exhibits large optical gap and exceptional ambient stability.The chemical doping with Sb was also carried out and a preferred occupation of Sb in the octahedral[InBr6]3-rather than the tetrahedral ones is observed.Upon UV-light excitation,red emission ascribed to STEs was detected in(C11H24N2)2[InBr6][InBr4]with large Stocks shift and wide full-widths at half-maximum(fwhm),and the PLQY is significantly enhanced from 8%to 61%after Sb doping due to the extra photo-induced excitons.Theoretical calculation indicates a direct-indirect gap transition after Sb doping in the system.3)A new OIMH(C13H14N)2InCl5(C13H14N+=N-methyldiphenyammonium)was synthesized,which is composed of unique trigonal bipyramid[InCl5]2surrounded by organic cations.(C13H14N)2InCl5 shows an optical band gap of 4.41 eV and exhibits blue photoluminescence.Both experiments and theoretical calculation indicate that the inorganic[InCl5]2-unit contributes to the blue emission.Remarkably,Sb3+doping in[InCl5]2-trigonsal bipyramid units induces a new dual-band emission at 540 and 735 nm,leading to tunable single-component white light emission in(C13H14N)2InCl5:xSb3+.The white light emission with x=1%doping content exhibits a high PLQY as 46.26%and more importantly,an ultra-high CRI up to 96.4)A new 0D tetrahedral Mn-based OIMH(ABI)2MnBr4(ABI= 2aminobenzimidazole)has been synthesized,which shows narrow-band green emission with fwhm=42 nm.(ABI)2MnBr4 is observed to spontaneously transform to the recently reported(ABI)4MnBr6 in ambient environment,which exhibits[MnBr6]4-octahedral coordination and bright red emission.Remarkably,we found that after a very small amount of Zn(5%)doped in the structure,this tetrahedron-to-octahedron transition is strongly suppressed and meanwhile its luminescent intensity is still maintained due to the small doping concentration,suggesting that Zn doping is an effective strategy to address the issue of the chemical stability of green-emitting(ABI)2MnBr4.5)Two 0D tetrahedral Mn-based OIMHs(MDPA)2MnBr4(1)(MDPA=Nmethyldiphenylaminium)and(MTPP)2MnBr4(2)(MTPP=methyltriphenylphosphonium)with narrow-band green emission have been synthesized,and the compound 2 shows narrower fwhm(48 nm)than 1(62 nm).It is demonstrated that the smaller hydrogen bond strength between organic and inorganic ligands leads to weaker distortion of inorganic tetrahedron,and further resulting in the narrower band emission.The TL behavior is also observed in both two compounds.Our work sheds light on the relationship between the organic ligand,hydrogen bond,structure parameter and the fwhm in Mn(Ⅱ)hybrids,which will benefit the design of new narrow-band green emitting OIMHs for the LCD application.