Research On Fluorescence Characteristic Of Bromine Lead Cesium Perovskite Nanocrystals

All-inorganic lead bromine perovskite nanocrystals?NCs?have interesting optical properties such as,narrow band gap,high photoluminescence quantum yield?PLQY?,large absorption range,high carrier mobility and slow auger recombination process,which attract extensive research.In this thesis,CsPbBr₃ NCs with different crystal structures and morphologies as well as its composite phase were obtained by thermal injection method.The relationship between crystal phases or morphologies and the fluorescence properties of NCs was studied and explained.The results are as follows:In the first part of this work,the formation of CsPb₂Br₅ phase accompanying CsPbBr₃quantum dots?QDs?was obtained by changing the ratio of precursor.And its influence on photoluminescence?PL?spectra of CsPbBr₃ QDs is discussed.The PbBr₂ ratio in synthesis of CsPb₂Br₅ phase is evaluated in which high proportion PbBr₂ seems like a key role on CsPb₂Br₅particles formation at the surface of cubic phase CsPbBr₃.The mechanism of CsPbBr₃ QDs PL intensity improvement by proper amount of CsPb₂Br₅ phase is elucidated through fluorescence lifetime curves.It is mainly because that the electron transfer process from the excited electrons of CsPb₂Br₅ phase with broad band gap to the conduction band of CsPbBr₃ QDs may increase the electron density.The second part work has pay attention to the relationship between NCs'morphologies and fluorescence emission.The effect of the propionic acid?PA?amount or carbon chain length on NCs'morphologies were systematically related to the its optical performance.It is found that the ratio of oleylamine?OAm?and PA is one of key factors in the growth of CsPbBr₃ NCs along the directions.When the molar ratio of OAm/PA deviates from 1:1,the growth of the crystal tends to along the?110?plane,presenting a sheet-like morphology.At OAm/PA ratio of 1:1,the shape of NCs exhibits a hexahedral morphology.The length of the carboxylic acid carbon chain also plays a role in the growth stage of NCs,the steric hindrance caused by different carbon chain lengths directly affects the growth rate of NCs.In relation to PL spectra and time-resolved spectra,the fluorescence peak wavelength has few connections with the morphologies,but PL intensity is obviously influenced by the crystal morphologies.The radiation recombination probability of the CsPbBr₃ NCs is related to the size decrease of the NCs.The third part in this dissertation focuses on the crystal phase composition of CsPbBr₃,CsPbBr₃-Cs₄PbBr₆,CsPbBr₃-CsPb₂Br₅ NCs and their temperature stability.The single NCs phase and mixed NCs could be obtained by controlling the ligand and precursor ratios.In considering the PL spectra,the mixed NCs including CsPbBr₃-Cs₄PbBr₆ and CsPbBr₃-CsPb₂Br₅ exhibit better fluorescence emission intensity and improve PL thermal stability from70 K to 373 K than that of CsPbBr₃.The irreversible thermal loss curves for the mixed NCs and single CsPbBr₃ NCs are compared in the range of 283-373 K,indicating the positive effect of addition of mixed phase on the PL properties of CsPbBr₃ NCs.