Dielectric Properties And Photoluminescence Properties Of Low-Dimensional Organic-Inorganic Hybrid Perovskites

The applications of phase transition materials in data storage,switching media devices,sensors and other fields are favored by scientists.In the search for multifunctional phase change materials,organic-inorganic hybrid perovskites are being studied by more and more researchers due to their simple synthesis and interesting tunable photoelectronic properties.A typical organic-inorganic hybrid perovskite is a metal halide perovskite with a 3D（three-dimensional）structure and is given the chemical formula ABX₃.The ability of A,B and X to form 3D structures is limited by many factors,the most important of which is the Goldschmidt volume factor,which becomes a huge obstacle to the preparation of 3D perovskite.However,low-dimensional perovskites are not limited by volume factors.By selecting suitable organic components,2D,1D and 0D perovskite can be obtained.At the same time,due to the flexible structure of organic-inorganic hybrid perovskite,this kind of materials is more prone to structural phase transition than traditional inorganic perovskite materials.Moreover,organic-inorganic hybrid perovskite has important application potential in luminescent materials,nonlinear optical materials,solar cells and other fields.Therefore,low-dimensional organic-inorganic hybrid perovskite-type multifunctional phase change materials are studied in this paper.The main research contents and results are as follows:（1）Four new zero-dimensional organic-inorganic hybrid compounds(C₆NH₁₆)₂Mn Br₄（1）,(C₇NH₁₈)₂Mn Br₄（2）,(C₁₆NH₂₈)₂Mn Br₄（3）and(C₁₉NH₃₄)₂Mn Br₄（4）were synthesized.Both compound 1,2,3 and 4 emit bright green light with quantum yields of 45.93%,50.98%,44.36%,71.41%,respectively,higher than most reported manganese（II）based compounds.The results show that adjusting the ligand cations can not only change the phase transition temperature,but also improve the fluorescence properties and achieve the purpose of increasing the quantum yield（PLQY）.These findings open up a new way to study Mn²⁺based low dimensional organic-inorganic hybrid compounds,especially phase change materials with switchable dielectric properties and excellent photoluminescence properties.（2）A pair of 1D organic-inorganic hybrid perovskite enantiomers,（R/S-3-HP）Pb Br₃（compound 5/compound 6）（3-HP=3-hydroxy-piperidine）were synthesized by solution method.Differential scanning calorimetry（DSC）and dielectric measurements showed that reversible phase transitions occurred at 349/336K.At the excitation wavelength of 339 nm,there was a wide emission peak at 635 nm,showing orange light.In addition,the indirect bandgap is 3.29 e V and the SHG intensity is comparable to that of KDP.This discovery provides a way to study multifunctional chiral perovskite materials.（3）2D lead-based perovskite(C₅NH₁₃Br)₂Pb Br₄（compound 7）(C₅NH₁₃Br=5-bromoamyl cation)was synthesized by introducing flexible chain organic cations.The evolution of ferroelastic domains observed by polarized light microscope confirms that compound 7 undergoes ferroelastic phase transition at 392/384 K.In addition,its direct bandgap is 2.877 e V.Interestingly,the material emits an attractive blue light（quantum yield 5.06%）under UV light.Three structural descriptors are introduced to quantitatively analyze the relationship between structural distortion and the shape of emission peak.This work provides a way to design multifunctional perovskite-type phase transition materials.