The Study Of Synthesis And Optical Properties Of CsPbBr₃ Microplatelets

Recently,benefiting from the excellent optical gain,high optical absorption coefficient,and long carrier diffusion length,metal halide perovskites show great application prospects in the fields of solar cells,light-emitting diodes(LED),lasers,photodetectors and other optoelectronic devices.However,there are still many problems in the study of metal halide perovskites,such as poor stability,easy degradation in humid and hot conditions,less deep study on photophysical problems and unclear emission mechanism which limit the wide application.Therefore,the preparation of high-quality metal halide perovskite micro-nanostructures and the study of photophysical properties are of great significance for commercial device applications.In this work,inorganic halide perovskite single crystalline structures such as microplatelets and nanowires have been fabricated by van der waals epitaxy,and the emission mechanism has been systematically studied by photoluminescence(PL)and lasing spectroscopy measurements.The main studies are list as bellow:1.Development of growth preparation and regulation of all inorganic halide perovskite CsPbBr₃ single crystal structure.These CsPbBr₃ single crystals have been grown by van der waals epitaxy and show highly stable under humid and hot conditions.By changing the growth conditions including reaction pressure,reaction temperature and substrate type,the morphology,size and distribution density of CsPbBr₃ are well regulated.2.The origin of double peaks in PL spectroscopy has been clarified for CsPbBr₃microplatelets(MPs)on mica.The power-dependent PL spectroscopy shows that the photon energy of the double PL peaks is invariant upon the exciting power,which indicates that both peaks are related to free exciton emission,excluding the possibility of bound exciton emission.The exciton binding energy of the double peaks are fitted to?41 me Vvia temperature-dependent PL spectroscopy,further demonstrating the same origin.Meanwhile,when the measuring temperature rises from 78 K to 294 K,the high-energy peak blue shifts while the low-energy peak red shifts,indicating the high-energy peak comes from the PL generated on the surface of CsPbBr₃ MPs,while the lower energy one is produced by PL leaking out from the edge of the MPs after multiple reflection by Mica substrate.With the increase of temperature,the lattice thermal expansion increases the band gap,which leads to the blue shifts of the high-energy peak,while the photon propagation loss will increase and leads to the red shifts of the low-energy peak.Moreover,the low-energy peaks can be obviously suppressed by changing the substrates of different refractive indices and under the method of space-resolved PL measurement,which further proves the conclusion.3.Combining the Fourier imaging system with the laser system,the angle-resolved lasing spectroscopy is used to explore the lasing mode of CsPbBr₃ MPs at room temperature.Though it's still controversial whether the lasing mode in CsPbBr₃ MPs originates from the in-plane Fabry-Perot(F-P)mode oscillation or the whispering-gallery-mode(WGM)oscillation,these two modes has been well identified by angle-resolved micro-PL Fourier imaging technique in this work.Meanwhile,In-plane F-P mode lasing transition to WGM lasing is verified at room temperature,which mostly occurs in large MPs with edge length(L)over 13?m.The F-P lasing is suppressed upon decreasing L or increasing excitation density,and the WGM lasing is predominant for all MPs at high excitation density.Furthermore,the parity and symmetry of in-plane F-P cavity modes are classified.These results not only open an alternative route to characterize semiconductor micro-cavity modes,but also solve the dispute about the origins of lasing modes.Further,it provides guidance for the development of lasing switches,photonic chips and polarization devices involving semiconductor planar micro-cavities.