Preparation And Optical Property Of Low-dimensional Perovskite Micro/Nanomaterials

In just a few years,the all inorganic cesium lead halide perovskite CsPb X₃（X=Cl,Br,I）as an emerging semiconductor has emerged in the optoelectronic fields of light-emitting displays,amplified spontaneous emission（ASE）and lasers.For the moment,it has been the focus of research because of excellent properties such as high optical gain(980 cm^-1),high absorption coefficient(1-4.5×10⁴cm^-1)and high quantum yield（90%）.However,the current situation of luminescence quenching caused by the internal octahedral structural unit[PbBr₆]^4-corner sharing is difficult to solve.It has been demonstrated that purposely engineering the topological network of metal halide perovskites to lower dimensions（e.g.,0-D,1-D,and 2-D）is a promising solution to suppress the PL quenching.In particular,the all-inorganic cesium lead zero-dimensional perovskite Cs₄PbBr₆fundamentally solves the problem of luminescence quenching,because its[PbBr₆]^4-is completely isolated by Cs⁺.However,the origin of its luminescence is not clear.Moreover,previous work on 0-D perovskites has focused on spontaneous emission,while stimulated emission properties and potential applications are rarely investigated.To further study on the structural characteristics,luminescence origin,phase change characteristics and lasing characteristics of Cs₄PbBr₆is of great significance for basic disciplines or further designing the Cs₄PbBr₆materials.The main findings are as follows:（1）CsPbBr₃ regular octahedral crystallites were prepared by a simple anti-solvent method,and they exhibited single-mode or dual-mode laser mode under picosecond laser pulse excitation.The lowest pump threshold achieved in the CsPbBr₃octahedral resonator is comparable to the previously reported pump threshold in a high-quality CsPbBr₃resonator excited by a shorter femtosecond laser pulse,which indicates that the developed CsPbBr₃octahedral microstructure is creating high-quality light-emitting devices have great potential.And it is found that the pump threshold intensity depends on the crystallite size,and smaller crystallites help low-threshold lasers.The experimental results are contrary to numerical simulations.We believe that the gain loss effect of the perovskite resonator,especially the intrinsic scattering loss It plays an important role in the preparation of laser devices.（2）For the CsPbBr₃ bulk material,the luminescence quenching caused by its internal structural unit[PbBr₆]^4-corner sharing limits its further application.The pure phase zero-dimensional Cs₄PbBr₆perovskite rhombohedral crystallites were successfully prepared by the same method.Its quantum yield is as high as～30%.In particular,the close relationship between the photoluminescence excitation spectrum and the local light absorption band provides direct evidence that visible photoluminescence originates from the excitation of Pb²⁺confined in the[PbBr₆]^4-octahedron.An electronic transition mechanism is initially proposed to explain the observed absorption and photoluminescence characteristics.Upon optical pumping with pulsed lasers,single-and multimode lasing are achieved in individual Cs₄PbBr₆perovskite microcrystals,showing a high photostability even upon rather intense optical pumping.The potential application to achieve spectral-free optical imaging is demonstrated by using a single Cs₄PbBr₆microcrystal laser as the illumination source.This study helps gain more insight into the nature of the visible photoluminescence observed in 0-D metal halide perovskites and inspires further applications.Zero-dimensional perovskite Cs₄PbBr₆and three-dimensional perovskite CsPbBr₃are prone to phase transition.At present,the poor stability of CsPbBr₃under polar conditions is still difficult to solve.Here,we propose a novel one-step method for the fabrication of low-cost,high-stability laser devices.The Cs₄PbBr₆cuboidal nanocrystals are induced into green-emitting CsPbBr₃cubic nanocrystals by water treatment.CsPbBr₃further autonomously generate more stable two-dimensional perovskite CsPb₂Br₅to protect the green-emitting three-dimensional perovskite CsPbBr₃nanocrystals.The two-component heterojunction CsPbBr₃&CsPb₂Br₅thin film achieves the ASE of green light pumped by a single photon picosecond laser at air environment.At the same time it could maintain outstanding stability in the water environment medium,and the material can maintain superior laser stability after multiple water treatments.Our work opens up a strategy for the stabilization of CsPbBr₃perovskites NCs without addition of foreign surface-passivating ligands in aqueous media.