| Lead halide perovskites have attracted extensive attention as promising materials in optoelectronic applications owing to their excellent optical and electric properties such as long carrier life time,strong optical absorption,tunable bandgap and high quantum yields.All-inorganic CsPbX3(X=Cl,Br,I)perovskites have good thermal and structural stability while reserving intriguing photoelectronic properties.As a member of the family,CsPbCl3 is a direct wide bandgap semiconductor.The crystal structure is very sensitive to temperature,and emission wavelength is located in blue-violet region.Up to now,CsPbCl3 crystals with various morphologies including quantum dots,films,sheets,wires or rods have been synthesized and used in near-ultraviolet photodetectors,lasers,and higher-order multiphoton fluorescent applications.However,there are few literatures about systematically studying and optimizing experimental parameters for morphology-controlled synthesis of CsPbCl3 micro-nano crystals by vapor deposition method.In our work,CsPbCl3 micro-nano crystals with different morphologies were prepared using a one-step physical vapor deposition method,and the structures and optical properties of CsPbCl3 micro-nano crystals were investigated by a variety of techniques.The results are as follows:1.The influence of various factors including evaporation temperature,growth temperature and time as well as substrate type on morphology of CsPbCl3 samples were systematically explored and discussed with CsCl and PbCl2 as the raw materials.It is found that the source powders in the quartz boat experience not only components evaporation but also solid-state chemical reactions during heating and the by-product Cs4PbCl6 is almost completely converted into CsPbCl3 when the temperature is raised to 600℃.The growth temperature plays an important role in controlling the morphologies and structures of the CsPbCl3 micro-nano crystals.As the growth temperature increases,the evolution process of morphologies is:irregular polyhedrons→large numbers of rods,pyramids,frustum of prisms with relatively sharp edges→fustum of prisms coexistence with platelets→platelets with smooth surface and sharp edges,some of which are conglutinated with each other→dendritic shape formed by distorted and wrinkled platelets.The micro-sized high-quality single crystal CsPbCl3 microplatlets were obtained at 450℃.In addition,the growth time has a great effect on sizes and particle densities of CsPbCl3 crystals.Prolonging the growth time leads to the increase of average grain sizes and obtaining large-sized CsPbCl3 single crystals,while the substrate makes very little difference to CsPbCl3 crystals.2.The CsPbCl3 individual microplatelet synthesized under growth temperature 450℃ was selected as the typical sample for the characterization of composition,structure and optical properties.The power and temperature dependent photoluminescence(PL)spectroscopy is performed to explore the emission properties of the CsPbCl3 microplatelet.It is found that the PL spectrum of the individual microplatelet displays an asymmetric structure consisting of a main peak at 412 nm and several shoulder peaks.The power and temperature dependent PL spectra of the CsPbCl3 microplatelet suggest that the excitation power only affects the emission intensity,while the temperature impacts the peak intensity,shape and position,implying that the thermal expansion of the lattice and exciton-optical phonon interaction dominate the change of the main peak together.The exciton binding energy of 79 meV is dertermined from Arrhenius equation.The PL spectra were fitted with five features by Gaussian function which can be attributed to free exciton,bound exciton,stimulated emission and surface defect related transitions,respectively. |
PDF Full Text Request