Synthesis Of Lead-Free Metal Halide Materials And Their Light-Emitting Applications

In recent years,lead-free metal halide perovskites and their derivatives have been flourishing in many emerging applications because of their benefits of reduced toxicity,excellent optical properties and low-cost solution processing methods.They have been widely used in light emitting diodes(LED),X-ray imaging,solar cells,lasers,photocatalysis and other hot research fields,which have made a series of research progress and breakthroughs.In this paper,the synthesis of two new lead-free metal halide perovskites materials is reported.The photophysicochemical properties and structural stability of the materials are improved through the exploration and optimization of key synthesis parameters.The key principles of property enhancement are clarified.Finally,the applications of high efficiency warm white LED and high performance X-ray imaging are realized.Because of the non-toxic property and the similar ionic radius to that of Pb2+,silver ion(Ag+)-containing perovskite derivatives have become an important class of Pb-free alternatives that are competitive for a variety of optoelectronic applications.While great success has been achieved in producing those Ag+-contained nanocrystals(NCs)by simple and low-cost solution method,such as Cs2AgInCl6 and Cs2AgBiCl6,colloidal synthesis of the pure Ag-based emitters has been rarely reported.Herein,we devise a facile europium chloride(EuCl3)-based route to CsAgCl2 NCs with tunable particle size and desirable warm white-light emission.To enhance optical property of CsAgCl2,we further demonstrate trace doping strategy with Sb3+,which boosts quantum efficiency of the resulting NCs from 16%to 39%.Moreover,the addition of Sb3+was found to significantly reduce particle size of the CsAgCl2 NCs from a few hundred nanometers to several nanometers as a result of the reduced surface energy,paving the way for the formation of emissive layers with well-controlled thickness and improved uniformity.Prototype electroluminescence devices fabricated using these nano-emitters exhibit favorable warm white-light emission,which opens up new avenues to develop single-component warm white light-emitting diodes.Different from Ag-based perovskite derivatives,Mn-based organic-inorganic hybrid metal halides are garnering increasing interest for use in X-ray imaging because of their high efficiency of X-ray absorption and radioluminescence.In addition,unlike most reported Ag halide self-trapping luminescence mechanism,Mn halide fluorescent materials mainly rely on internal Mn d-d orbital transition(4T1→6A1),so it is easier to shield environmental influences and obtain efficient fluorescence emission.In fact,some Mn halides have obtained more than 90%PLQY without dependence on foreign atom doping.However,no universal synthesis has been reported that allows all their Cl-,Br-,and I-compositions to obtain photoluminescence quantum yield(PLQY)approaching 100%that is necessary for superior scintillation properties.Here,we present an efficient spacer cation that allows all their halide compounds to achieve high PL efficiency(PLQYs of 95%～98%)through the design of molecular structure and function.Moreover,the resulting crystals maintain stable phase for over 2 months in ambient air,which surpasses most other all-inorganic counterparts.A representative scintillator displays X-ray imaging performance with high light yield of 44000 ph/MeV and low detection limit of 0.64 μGy/s,better than that of the commercial LuAG:Ce scintillator crystals(2,000 ph/MeV,2.32 μGy/s).