Luminescence Properties And Growth Mechanisms Of Different Crystal Structures Of Perovskites And Their Composites

The inorganic lead halide perovskite nanocrystals（NCs）have attracted great interest owing to their superior optoelectronic properties.They have the virtues of narrow emission lines,high quantum yields,and tunable emission wavelengths in the visible spectral region.Therefore,they have good application potential in the fields of light-emitting diodes,lasers,solar cells,and photodetectors.On the other hand,the composite nanomaterials based on the perovskites have special structures,and they can enlarge the application areas of the perovskites.Therefore,the researchers have begun to study the perovskite-based composite NCs.The perovskites have different crystal structures.Compared with the common cubic structured perovskites,people know little about the properties of the perovskites with other crystal structures.They have big potential of research and development.The studies of the perovskite NCs can help to understand their various physical properties as well as can help to lay the theoretical foundation for their applications in the optoelectronic devices.The perovskite NCs are ideal materials for the fabrication of various nanodevices owing to their excellent optoelectronic and ferroelectric characteristics.The hetero-NCs can play a unique role in the nanodevices.Considering the large lattice match between the CsPbBr₃ and Cs crystals,we study the epitaxial growth of the Cs/CsPbBr₃ metal–semiconductor hetero-NCs in the solution.It was found that the very thin well-crystallized Cs single crystal layer can grow epitaxially on the surface of the CsPbBr₃ NC.Through calculation of the elastic potential energy in conjunction with consideration of the near-coincidence site theory,we explain the mechanical properties of the Cs/CsPbBr₃ hetero-nanocrystals,including their structural stability.These metal–semiconductor hetero-NCs have the application potential in the perovskite-based nanodevices.Compared with the cubic-structured CsPbX₃（X=Br,Cl）crystals,the Cs₄PbX₆ crystals with trigonal structure have larger bandgaps and distinct optical properties.Up to date,little has been known about the luminescence properties of the Cs₄PbX₆ NCs.We synthesized the well-crystallized Cs₄PbBr₆ and Cs₄PbCl₆ NCs,they have robust near-UV luminescence at room temperature,exhibiting remarkable quantum confinement effect.By using the experiments in combination with the first-principles calculations,we found that the near-UV luminescence of the Cs₄PbX₆ NCs originates from the Frenkel excitons trapped by the isolated PbX₆^4-octahedrons.The Cs₄PbX₆ NCs have large luminescence Stokes shift,being much larger than that of CsPbX₃ NCs.We explained the origin of such large Stokes shift by using the model based on the lattice relaxation theory.These wide-bandgap trigonal inorganic perovskite NCs with near-UV luminescence have application potential in short-wavelength optoelectronic devices.