Tuning Luminescence Properties Of 2D Organic-inorganic Metal Halides By Doping Strategy

Two-dimensional(2D)organic-inorganic metal halides(OIMHs)exhibit excellent photophysical properties(such as:White light emission,organic room-temperature phosphorescence,etc.),due to their inorganic multi-quantum well structure,tunable energy levels and the energy transfer between inorganic and organic part.Additionally,good solution-processability,thermal stability and moisture resistance of 2D layered OIMHs with the exceptional potential in white-light-emitting diodes(WLEDs),anti-counterfeit technology,information storage and bio-imaging.In this paper,phenylethylamine lead(zinc)halides as a host to regulate its luminescence properties by doping strategy,and explore the photoluminescence mechanism.The main innovation points of the research are as follows:Chapter 1:Phenylethylamine lead bromide as a host by doping halogens,to obtain a series of mixed-halide 2D white light-emitting hybrid perovskites(WHPs):(C₆H₅C₂H₄NH₃)₂Pb Br_xCl_4-x(0<x<4).With the increasing content of Br,the quantum yields of the WHPs increase gradually from 0.2%to 16.9%,accompanied by tunable color temperature ranging from 10000 K(“cold”white light)to 4000 K(“warm”white light).Steady-state fluorescent spectra at room temperature and low temperature,as well as transient fluorescent characteristics were studied to explore energy transfer between free excitons and self-trapping excitons,and the corresponding white-emissive mechanism.When applied in the WLEDs,the mixed-halide perovskites exhibit white electroluminescent emission with very high CRI of 87-91.Chapter 2:1,8-naphthalimide(NI),a common organic fluorophore,is doped into organic cations of 2D phenylethylamine lead halides(perovskites)to yield thin films and powders with yellow room-temperature phosphorescence(RTP)of NI in air.The triplet excitons of NI are mainly derived from Wannier excitons of inorganic part through energy transfer(ET)for films,and from singlet excitons of NI through intersystem crossing(ISC)for powder.Consequently,the quantum yield(?_P),lifetime(?)and color of RTP can be tuned by changing fluorophore and halide in perovskites,as well as solid morphology.A white emission comprising blue one from perovskite and yellow RTP(?_P=25.6%,?=6.3ms)from NI,are obtained in Br-based perovskites in powder.Cl-based perovskites exhibit fluorescent/phosphorescent dual emission in thin films,and yellow afterglow phosphorescence in powders(?_P=56.1%,?=35 ms).The unique performance of the perovskites with RTP can make them widely apply in the field of information technology as security ink,and white and afterglow LEDs as single luminescent materials.Chapter 3:Usually,enhancing the phosphorescence efficiency of organic materials causes a short lifetime.As described in Chapter 2,a highly efficient phosphorescent emission with the maximum?_P of 56.1%was obtained.However,their?of phosphorescence is below 50 ms,due to the effect of heavy atom of Pb.Here,we report two kinds of OAMs,2D layered organic-inorganic hybrid Zinc bromides(PEZB-NTA and PEZB-BPA),obtained in an environmentally friendly ethanol solvent by low-temperature solution method.They display highly efficient and persistent room-temperature phosphorescence emission(?>150 ms,?_P>40%in crystals;?>150 ms,?_P>25%in films)in air.For OAMs,the two quantum yields are one of the highest values ever reported for crystals and films,respectively.Due to the excellent crystalline and film-forming ability,PEZB-NTA and PEZB-BPA in ethanol can be used as ink to construct patterns in various rigid and flexible substrates,including paper,iron,plastic,marble,tin foil and cloth.Consequently,the novel OAMs show great application prospects in the field of anti-counterfeiting and information storage for economic synthesis,solution processing,and easy operation.Chapter 4:Organic fluorophore named as NLAC is introduced into 2D organic-inorganic metal halides(OIMHs)with wide band-gap(>3.54 e V)to give a green emission with quantum yield up to 81%.The highly efficient luminescence is ascribed to avoiding the aggregation of NLAC and formation of inorganic free exciton which is easy to be thermally quenched.On this basis,a new strategy to generate efficient white emission with afterglow has been proposed by co-doping short-wavelength fluorophore and long-wavelength phosphor into 2D Phenylethylamine lead chloride(PEPC).As a result,a single-component white-light-emitting material PEPC-3N based on NLAC with CIE of(0.33,0.36)and quantum yield up to 43%can be obtained.Interestingly,PEPC-3N shows a dual-color organic afterglow and excitation-wavelength dependent emission,consequently forming a switch between green fluorescence,white light and yellow afterglow.These unique performances impose PEPC-3N huge potential in afterglow WLED and information storage.Moreover,this white-light strategy is universal,and effective in Zn-based metal halide system.