Luminescence Mechanism And Thermal Stability Of All Inorganic CsPbX₃ Perovskite Quantum Dots

Semiconductor quantum dots has been widely used in the field of optical detection,photocatalysis,radiation detection,biological marker and solar cell etc.because of their solution preparation,easy processing,size-tunable emission and high quantum yield.The heavy metals,such as cadmium,based quantum dotshave a serious pollution to the environment.Therefore,all inorganic perovskite materials with low toxicity and environmental protection have become one of the research hotspots.Recently,all inorganic perovskite CsPbX₃?X=Cl,Br,I?quantum dots with the optical properties of size-and composition-tunable luminescence,narrow emission width and high luminous efficiency,which make them have broad application prospects in the field of lighting and display.Although the perovskite quantum dots themselves have so many advantages,there are some serious problems in the process of market production and application,because perovskite quantum dots are very sensitive to water,light and heat,resulting in fluorescence quenching,which degenerates the electrical and optical properties of the quantum dots.Therefore,they restrict their application and development in the field of lighting and display.In order to make the perovskite material have a better prospect of application,it is necessary to systematically study the thermal,light and chemical stability of the perovskite.In this paper,CsPbBr₃ and CsPbCl₃ quantum dots have been prepared.The luminescent mechanism of all inorganic perovskite quantum dots has been studied deeply,and the luminescent thermal stability of all inorganic perovskite quantum dots has been further studied.The main contents are as follows:1.All inorganic perovskite CsPbBr₃ and CsPbCl₃ quantum dots in solution were synthesized by hot injection.The CsPbBr₃ quantum dots with luminescent peaks located at 492 and 517 nm and the CsPbCl₃ quantum dots with luminescent peaks located at 398,405,and 407 nm were synthesized by adjusting the amount of ligand,reaction temperature and reaction time.The average particle sizes of the CsPbBr₃quantum dots with 492 and 517 nm emissions measured by transmission electron microscopy are 5.5 and 13.7 nm andthe average particle sizes of the CsPbCl₃ quantum dots at 405 and 407 nm are 6.1 and 9.9 nm,respectively.2.The thermal degradation mechanism of CsPbBr₃ quantum dots was studied by temperature-dependent photoluminescence?PL?spectroscopy.The CsPbBr₃ quantum dot films with emissions of 492 and 517 nm were treated at different temperatures under vacuum.It was found that when the thermal annealing temperatures reached320 K,the luminescence intensity of the quantum dots films decreased obviously.The transmission electron microscopy,X-ray diffraction and PL spectroscopy demonstrated that the size of quantum dots almost kept constant at thermal annealing temperatures below 360 K while it significantly enlarged at higher thermal temperatures above 380 K.The PL intensities,peak energies and linewidths of the annealed quantum dots films,as a function of temperature,are discussed in detail.The PL quenching of quantum dots films after heat treatment is due to the loss of surface ligands and the formation of a radiation free recombination centers in quantum dots.The PL degradation of the quantum dots was related to the formation of nonradiative recombination centers due to the loss of ligands and growth of quantum dots under thermal annealing.3.The luminescence mechanism of CsPbCl₃ quantum dots thin films was studied.The photoluminescence spectra,fluorescence decay curves,temperature-dependent PL spectroscopy and decay curves of the CsPbCl₃ quantum dots with emissions of398,405,and 407 nm were measured.According to the fluorescence lifetime at different energy,the fluorescence lifetimes of of three quantum dot samples were found to be almost invariable at the low energy side.With the increase of emission energy,the fluorescence lifetimes is obviously shortened.This indicates that the recombination luminescence of CsPbCl₃ quantum dot films is mainly from exciton localization.In addition,the average fluorescence lifetime first increased and then decreased with the increase of temperature,indicating the existence of localized or surface states in CsPbCl₃ quantum dot films.