Study On Luminescence Regulation And Application Exploration Of Several Metal Halide (Quasi-) Perovskites

Metal halide perovskites（MHPs）have become a hot research object in the field of materials science due to their excellent optoelectronic properties.Due to their tunable spectrum,high fluorescence quantum yield（PLQY）,wide absorption spectral range and long carrier diffusion length,MHPs have broad application prospect in light-emitting diodes and solar cells.In addition,MHPs also has great application potential in the fields of anti-counterfeiting,lasers,sensing,detection and photocatalysis.Exploring new applications of MHPs has become a new goal and challenge.In order to achieve this goal,new properties of MHPs can be designed by endogenous modification of crystal structure or exogenous construction of composite materials and regulation of surface interface properties to explore more application possibilities of MHPs.Therefore,many quasi-perovskite structures with new properties have been derived.The metal halide perovskite structure mentioned in this paper is the general name of perovskite structures and quasi-perovskite structures.In this paper,a series of research work is carried out around the design new luminescence phenomena of MHPs and their derivatives and the exploration of their applications,including the following three aspects:（1）Solvent-induced luminescence property regulation of CsMnCl₃·2H₂O and its application in anti-counterfeitingA quasi-perovskite single crystal CsMnCl₃·2H₂O with solvent-induced discoloration effect was synthesized.When the sample is contacted with N,Ndimethylformamide（DMF）or N,N-dimethylacetamide（DMAC）,its luminescence rapidly changes from red to bright green,and finally back to red.This process is accompanied by the transformation of the crystal structure from CsMnCl₃·2H₂O to Cs3MnCl5 to Cs2MnCl₄·2H₂O.The change of the luminescence color is due to the change of the coordination number of manganese（Ⅱ）during the phase transition process,and the stronger the crystal field strength,the more red-shifted the luminescence.Both the test paper and the printed pattern made of the CsMnCl₃·2H₂O have a fast response to DMF/DMAC,which makes this material have potential application prospects in anti-counterfeiting and information encryption.（2）Dual-mode luminescence of NaYF4:Er3+,Yb³⁺@CsMnCl₃ Core-shell nanocrystals（NCs）and its application in anti-counterfeitingManganese-based quasi-perovskite CsMnCl₃ NCs were prepared and grown on the surface of up-conversion nanoparticles(NaYF4:Er3+,Yb³⁺)to obtain a uniform coreshell heterostructure.This nanocomposite exhibits different luminescence under the irradiation of ultraviolet light and infrared laser,and is expected to be used for information encryption or anti-counterfeiting.We controlled the preparation conditions of CsMnCl₃ NCs,and under the optimal preparation conditions,samples with uniform particle size were obtained,and the luminescence mechanism was explained.Then,we discuss the heterostructure of the manganese-based perovskite/up-conversion nanocomposite and investigate the atomic connection of its heterojunction.The rationale for the two materials to form a heterostructure is demonstrated.Finally,we propose the possible application of the nanocomposite in anti-counterfeiting and information security by using the dual-mode luminescence.（3）CsPbX₃ NCs luminescence blue shift induced by polymer ligandWe designed and synthesized the polymer ligand P-A.After adding P-A to the colloidal solution of CsPbX₃（X=Br,I）nanocrystals（NCs）,the luminescence of CsPbX₃ NCs will undergo a blue shift,and the degree of blue shift increases with the increase of the amount of P-A added.The polymer ligand P-A has three functions:①The carboxylic acid and amide groups on P-A can replace the original ligands oleic acid and oleylamine to fully connect to the surface of the perovskite;② The double bonds at the end of the polymer ligand can interact with each other.Cross-linking or connecting other functional groups;③ Long alkyl chains can prevent nanocrystal agglomeration and keep the colloidal solution stable.We confirmed that the polymer ligands replaced the original surface ligands（oleic acid and oleamine）and had a shearing effect on the NCs.Due to the enhanced confinement effect,the emission of CsPbX₃ NCs blue-shifted,and then self-assembled to obtain CsPbBr₃@P-A colloids with uniform particle size.The solution narrows the emission peak and improves the color purity.