High Pressure Research On The Properties And Structures Of All-Inorganic Perovskite Materials With Different Morphology And Size

In recent years,halide perovskite materials have developed rapidly in light emitting diodes,lasers,photodetectors due to their unique optical properties,such as high carrier mobility,high photoluminescence quantum efficiency and adjustable band gap.Therefore,halide perovskite materials have attracted great attention of researchers.However,the inherent challenges of perovskite materials still exist,such as low stability and toxicity,which still need to be solved.This requires exploration and understanding the fundamental mechanism behind the excellent properties of perovskite materials.High-pressure technology is of great significance for studying and exploring the relationship between the properties and structures,which is widely used to explore new structures and properties of various materials.High pressure technology can effectively adjust the atomic spacing,electronic orbit and crystal structure of perovskite materials,and make them exhibit many interesting phenomena such as phase transition,band gap adjustment,metallization and induced luminescence under high pressure.In this paper,three representative inorganic halide perovskite materials are selected for research,they are Cs Pb Cl₃ perovskite nanosheets,Cs₂Te Cl₆ perovskite microcrystals and Yb³⁺ion-doped Cs Pb Cl₃ perovskite quantum dots.From the perspective of morphology,dimension and composition,the relationship between their properties and structural changes under high pressure is comprehensively and systematically studied using in-situ high pressure experimental technology and theoretical calculation.The main results of this paper are as follows:1.Phase transition and optical characteristics of all inorganic Cs Pb Cl₃ perovskite nanosheets were systematically studied by using high-pressure fluorescence,UV-visible absorption,Raman and X-ray diffraction combined with theoretical calculations.The results show that Cs Pb Cl₃ perovskite nanosheets show significantly enhanced broadband self-trapped exciton luminescence under high pressure.The fluorescence color changes from blue to red under high pressure,and the band gap decreases then increases.The structure undergoes an isomorphic phase transition from cubic phase（Pm-3m）to cubic phase（Pm-3m）,followed by amorphization.In addition,theoretical calculations show that the unique fluorescence phenomenon of Cs Pb Cl₃ perovskite nanosheets is due to the distortion of the inorganic octahedron,which effectively enhances the exciton-phonon interaction,inhibits the radiation recombination of free excitons and makes more self-trapped excitons stable,and enhancing the emission of self-trapped excitons.The contraction of Pb-Cl bonds under pressure leads to the decrease of Cs Pb Cl₃ band gap,and the tilting and twisting of inorganic octahedron leads to the increase of its band gap.These results show that the optical properties of Cs Pb Cl₃perovskite nanosheets under high pressure are closely related to their structural changes.2.The structure and optical properties of lead-free halide perovskite Cs₂Te Cl₆microcrystals were investigated by high pressure fluorescence,UV-vis absorption,X-ray diffraction,Raman experiments and theoretical calculations.It is found that Cs₂Te Cl₆ perovskite microcrystals exhibit structural stability under pressure,and maintain the cubic structure of Fm-3m space group without phase transition.The fluorescence peak of Cs₂Te Cl₆ perovskite microcrystals continues to blue shift and finally disappears under pressure.The continuous reduction of the band gap is due to the continuous contraction of the[Te Cl₆]^2-octahedron under pressure.It is found that the Huang-Rhys factor of Cs₂Te Cl₆ perovskite microcrystals decreases under pressure,indicating that the electron-phonon coupling strength decreases gradually.The blue shift of fluorescence peak may be caused by the decrease of lattice relaxation energy.These results contribute to a better understanding of the structure and physical relationship of perovskite materials under high pressure.3.The optical properties and crystal structure changes of Yb³⁺-doped Cs Pb Cl₃quantum dots were investigated by high pressure fluorescence,UV-visible absorption and synchrotron XRD.The phase transition from cubic phase to cubic phase occurred at 1.93 GPa.The fluorescence peak of Cs Pb Cl₃ matrix continued to redshift and weaken under pressure,and finally disappeared at 1.54 GPa.The fluorescence peak corresponding to the ²F_5/2—²F_7/2 transition of Yb³⁺ions gradually weakened under pressure and finally disappeared at 1.46 GPa,indicating that the optical properties of Yb³⁺ions was affected by the external lattice environment.The pressure-induced near-infrared fluorescence quenching of Yb³⁺ions may be related to the destruction of resonant energy transfer process.The band gap of the sample decreases first and then increases under high pressure,which may be caused by the isotropic contraction of Pb-Cl bond and the deformation of[Pb Cl₆]^4-octahedron.These results further enrich our understanding of the structure and fluorescence characteristics of rare earth doped luminescent materials under high pressure.These results enrich our understanding of the structure and properties of rare earth doped luminescent materials under high pressure.