| All-inorganic metal halide perovskites have been widely used in light-emitting diodes and solar cells due to their excellent features,including high photoluminescence quantum yields,high charge carrier mobilities,high absorptions coefficients,and narrow and tunable emission.However,the main obstacle is the poor stability of perovskites under temperature,humidity,oxygen,and light,which can easily destroy the crystal structure of perovskites.There are a lot of defects in the crystal and surface of metal halide perovskites,and the ligands are labile,which greatly reduces the photoluminescence quantum yields of perovskites.In addition,the toxicity of lead halide perovskites cannot be underestimated,which seriously threatens the environment and human health.In this paper,low-dimensional perovskites synthesis,matrix encapsulation,ions doping,and lead-free double perovskite replacement are adopted as the strategies to effectively improve and enhance metal halide perovskites.The main contents are as follows:1.Zero-dimensional perovskite Cs4PbBr6 microcrystals with uniform hexagon prism morphology and high photoluminescence quantum yields were synthesized via a facile precipitation method.The ratio of Cs and Pb and the amount of ligand have a significant effect on the size and luminescence properties of Cs4PbBr6.The ligand content plays a dominant role in the solubility of PbBr2 and can compete with Cs+ions for the surface passivation of Cs4PbBr6 microcrystals,thus modulating the kinetics of the reaction to influence the size and phase of final product.Meanwhile,Cs4PbBr6 microcrystals have good stability and still maintain stable phase and good luminescence properties after several thermal cycling treatments and long-time exposure to atmospheric environment.Highly emissive hexagonal Cs4PbBr6 microcrystals with excellent stability were used as phosphors for white light-emitting diodes,and the luminous efficiency of the white light-emitting diode device was determined to be as high as 116.84 lm W-1.2.The CsPbX3/PbWO4 composites were prepared by ion adsorption and in-situ growth method with leaf-like PbWO4 as the matrix.There are many defects and voids in the crystal structure of PbWO4 matrix,which provide nucleation growth space for CsPbX3.Besides,the lattices of CsPbX3 and PbWO4 match each other,and CsPbX3 and PbWO4 connected by chemical bonding to form the stable CsPbX3/PbWO4 composites.Due to the protection of PbWO4,the CsPbX3 in the composites exhibits excellent stability,and can maintain good luminescence properties under several thermal cycling treatments and long-time exposure to air and ultraviolet lamp irradiation.In addition,the light-emitting diodes devices based on CsPbX3/PbWO4 composites have good performance,which indicates CsPbX3/PbWO4 composites have great potential in lightemitting diodes field.3.Ti3+ ions doped CsPbCl3 nanocrystals with good monodispersity were synthesized by an improved hot-injection method.The occurrence of non-radiative recombination in CsPbCl3 nanocrystals could be effectively reduced by doping heterovalent Ti3+ions,which significantly improved the photoluminescence intensity and photoluminescence quantum yields of CsPbCl3 nanocrystals.Density functional theory calculations reveal that Ti3+ ions could introduce more band-edge states around the conduction band minimum of CsPbCl3,which is conducive to release electrons into conduction band.Furthermore,Ti3+ion doping could inhibit the Cl vacancy concentration in CsPbCl3 and prevent the in-gap state caused by Cl vacancy.In addition,the stability of CsPbCl3 perovskite is greatly improved through Ti3+ion doping.4.The rare-earth-based halide double perovskite Cs2NaRECl6(RE=Tb,Eu)nanocrystals with monodisperse and uniform size were synthesized by hot-injection method.Cs2NaRECl6(RE=Tb,Eu)double perovskite nanocrystals have multiple emission peaks,corresponding to the photoluminescence from halide double perovskite host and from the f-orbitals in rare earth ions(Tb3+ and Eu3+).Temperature-dependent photoluminescence spectra show that Cs2NaRECl6(RE=Tb,Eu)double perovskite nanocrystals have good thermal stability.In addition,the as-synthesized Cs2NaRECl6(RE=Tb,Eu)nanocrystals exhibited excitation-wavelength-dependent multicolor emission.The rare-earth-based Cs2NaRECl6(RE=Tb,Eu)double perovskite nanocrystals with wide color gamut emission and excellent luminescence properties exhibit great potential in anti-counterfeiting information code and light-emitting diodes. |
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