Preparation Of Manganese(Ⅱ)-based Perovskite And Application In Solvent Detection

Metal halide perovskite has attracted the attention of researchers in various fields because of its simple fabrication process,adjustable emission spectrum,excellent charge transfer and high theoretical photoelectric conversion efficiency.Most of the perovskite materials reported at present contain lead.Considering that lead is extremely toxic to the environment,it is of great significance to develop lead free perovskite materials with low toxicity and high photoluminescence quantum efficiency.Manganese（II）-based perovskite materials show certain advantages among the candidates of lead-free perovskite materials because of their multi-iron properties,phase-change memory and luminescence tunability.In addition,manganese（II）-based perovskite with phase change sensitive photoluminescence color has attracted extensive attention in the field of sensing and detection,and some achievements have been made.However,the research of this kind of perovskite materials is still in the preliminary stage,and there are still many challenges in material preparation,luminescence properties and applications.This thesis focuses on the study of manganese（II）-based perovskite.Two types of manganese（II）-based perovskite materials with high photoluminescence quantum efficiency and solvent-induced phase transition characteristics are prepared.The structure,morphology and optical properties of the materials are studied and applied in the field of visual detection.In details:Firstly,Cs_xMn Br_x+2 crystals with solvent-induced crystal discoloration were prepared and successfully applied to the recognition of ethanol and methanol.In this thesis,two kinds of perovskite crystal materials Cs Mn Br₃ and Cs₃Mn Br₅ were prepared by solvent evaporation crystallization method.The six-coordination Cs Mn Br₃ crystal showed photoluminescence emission peak at 625 nm,and the photoluminescence quantum efficiency was 4.5%.However,the Cs₃Mn Br₅ crystal has a photoluminescence emission peak at 518 nm,and its photoluminescence quantum efficiency reaches 69%.Using ethanol as an external stimulus,the reversible conversion between 625 nm emitting Cs Mn Br₃ and 518 nm emitting Cs₃Mn Br₅ was successfully achieved.However,methanol only destroys the crystal structure of Cs Mn Br₃ and makes it luminescence quenching.Therefore,the recognition of ethanol and methanol can be realized by using solvent induced crystal discoloration,which solves the problem that methanol and ethanol are difficult to distinguish.Secondly,lead-free DMA_xMn Br_x+2 perovskite crystal with high photoluminescence quantum efficiency was prepared by DMA⁺instead of Cs⁺.DMAMn Br₃ with octahedral structure produced photoluminescence emission at 610 nm and the photoluminescence quantum efficiency was 41%.The photoluminescence emission of DMA₂Mn Br₄with tetrahedral structure near 517 nm was as high as 70%,which was 10 times of the maximum value reported in the literature.In addition,the prepared DMAMn Br₃ crystal was very sensitive to water,and the photoluminescence shifted from 610 nm to 517 nm in only a few tens of seconds after exposure to wet environment.The experiment verified that the crystal also changed from six-coordination DMAMn Br₃ to four-coordination DMA₂Mn Br₄ structure.The reversible conversion between DMAMn Br₃ crystal and DMA₂Mn Br₄ crystal was realized through the introduction and volatilization of water molecules.DMA_xMn Br_x+2 perovskite crystals were dispersed into non-luminescent matrix Ca F₂,and the crystal was sensitive to external moisture at low concentration.