Study On The Synthesis,Photoluminescence Tuning And Mechanism Of Metal Chloride Perovskite With Broad-band Emission

In recent years,metal halide perovskites have been widely used in light-emitting diodes and other optoelectronic fields due to their adjustable emission spectra,high-efficiency fluorescence quantum yield,and simple solution preparation.In particular,the introduction of broad-band emission in materials expands the range of materials,which is expected to be used in multi-color broadband light-emitting devices,high-efficiency continuous spectrum tunable lasers,X-ray scintillators,thermometers,photodetectors,fluorescence sensors and waveguides.However,there is still a lack of systematic research on the luminescence mechanism and performance regulation of broad spectrum emission,and the relationship between its structure and properties is still unclear.In addition,the toxicity and poor stability of lead-based materials still need to be resolved.Metal halide perovskites provide a versatile platform for manipulating photoluminescence due to their multifarious crystal structures,chemical compositions and morphologies.Based on this,the research contents are including mainly two aspects:on one hand,adjusting the broadband emission of the material in different ways and explore its luminescence mechanism;on the other hand,synthesizeing lead-less or lead-free halide perovskite materials.The specific research work is as follows:1.Synthesis and Optical Properties of Heavily Mn-doped CsPb Cl₃ NCsIn this work,we successfully synthesized CsPb_1-xMn_xCl₃ nanocrystals（NCs）with high manganese content,and achieved wide orange-red light emission（600 nm～653nm）tuning.Higher manganese content introduces more defects,resulting in an increase in non-radiative recombination centers,so the material has poor luminescence properties.The PL QYs of CsPb_0.1Mn_0.9Cl₃ NCs is about 5.6%.Then,the high content of manganese is composed of isolated core,surface-bound and an agglomerated phase of strongly interacting Mn²⁺ions,called Mn²⁺_core,Mn²⁺_surf and Mn²⁺_agg,respectively.The local uneven distribution of Mn²⁺leads to a larger degree of lattice disorder,which is the main reason for the low PL QYs.In addition,the local uneven distribution of Mn²⁺in NCs bring about local lattice rearrangement,thereby alleviating the disorder of the crystal lattice to a certain extent,and the defect state of the deep level is passivated.As a result,the PL QYs of Mn²⁺emission increased greatly,the proposed NCs successfully achieved 67.86%of the highest PL QYs after 30 days and shows extremely high strong air stability for over 160 days.This work has a further understanding of the doping mechanism and defects of Mn²⁺.2.Water-induced In-situ Reversible Luminescence of Organic-inorganic Hybrid（C₆H₅NH₃）MnCl₃ Single CrystalsA new one-dimensional manganese-based（C₆H₅NH₃）MnCl₃ single crystal was synthesized by a simple cooling crystallization method.Through transient,steady-state transient spectroscopy and fluorescence spectroscopy of different excitation powers,the red broadband emission（685 nm）came from d→d*transitions of[MnCl₆]^4-octahedron,and PL QYs is 9.6%.In addition,the red light-emitting（C₆H₅NH₃）MnCl₃absorbs water in situ and undergoes structural transformation,and finally turns into a new green light-emitting material.Using fluorescence spectroscopy,XRD diffraction and morphology studies,the reversible change process of water absorption and dehydration was studied,and it was speculated that the new green light-emitting material was（C₆H₅NH₃）MnCl₃.H₂O.Then,（C₆H₅NH₃）MnCl₃.H₂O was directly synthesized by solvent volatilization,and found that the introduction of H₂O changed the coordination environment of Mn²⁺,and the PL QYs was increased to 15.7%.This work broadens the understanding of the luminescence mechanism of manganese-based halide,and has certain reference significance for the design and synthesis of lead-free manganese-based luminescent materials in the future.3.Synthesis and Photoluminescence Mechanism of Tin-doped CsCdCl₃ with Deep-Red EmissionIn this work,for the first time,hexagonal CsCdCl₃ was synthesized by a simple hydrothermal method.It showed very weak two kinds of STEs emission at room temperature,which are located in the green emission（STEs 1）and the near-infrared emission（STEs 2）.By doping a small amount of non-luminescent metal tin(Sn²⁺)ions,a CsCdCl₃:x Sn²⁺single crystal with deep-red emission（730 nm）was obtained,and the highest PL QYs was 28.22%.Through transient,steady-state and low-temperature variable-temperature fluorescence spectroscopy to study its luminescence mechanism,it is found that the material only exhibits STEs 2 luminescence in the low-temperature region.The broadening of the emission spectrum and the enhancement of intensity are also attributed to the introduction of impurity Sn²⁺.The introduction of impurity Sn²⁺is speculated to enhance the interaction between exciton accumulation and strong exciton phonon coupling,provides an additional effective exciton relaxation pathway to promote the radiation transition of STEs 2,and successfully achieves the regulation of multiple STEs emission.In addition,the synthetic material exhibits good stability,thermal stability and air stability.This work proves the development potential of CsCdCl₃ as a halide perovskite luminescent material,also provides samples for the luminescence mechanism and regulation of STEs.