Study On The Synthesis Of All-Inorganic Lead Halide Perovskite Nanocrystals

Perovskite nanocrystals?PNCs?possess low preparation cost,wide absorption spectrum,narrow and tunable fluorescence spectrum across the full-visible spectral range,and high photoluminescence quantum yields?PLQYs?,which has attracted much attention as a new class of semiconductor materials in recent years.Therefore,this paper focuses on the preparation of all-inorganic perovskite nanocrystals.By optimizing the synthetic route and developing new synthetic methods of PNCs,the optoelectronic performance is enhanced,the stability is improved and the toxicity is reduced,facilitating optoelectronics and biological imaging applications.In the second chapter,we firstly synthesized CsPbX₃?X=Cl,Br or I?NCs by microwave-assisted methods with bis?2,4,4-trimethylpentyl?phosphonic acid as ligands.By optimizing the types and dosage ratios of cesium precursors,ligands,and lead halides,the fluorescence emission of as-prepared CsPbX₃ NCs can be adjusted in the range of 400 nm to 700nm with the PLQYs of 90%,especially the significantly improved stability of CsPbI₃ NCs.We further used the ZnX₂ aqueous solution as anion-exchange reagent and assisted by ultrasound to accurately adjust the fluorescence emission of PNCs at intervals of 1 nm.The as-prepared NCs have good phase/chemical stability.Quantitative and high reactivity of halogens in anion-exchange reactions are the key to accurate and successive PL adjustment.Ultrasound promotes the blending of water and oil phases and increases the rate of anion-exchange reactions.The current efforts experimentally prove that the PL emission of CsPbX₃ NCs can be accurately and successively controlled like conventional semiconductor NCs,making perovskite NCs more competitive in illumination and display.In the third chapter,in order to further reduce the lead content and toxicity in PNCs,CsPb_xMn_1-xCl₃ NCs with a high proportion of Mn substitution were respectively prepared by hot-injection,microwave-assisted,and room-temperature ligand-assisted reprecipitation synthesis methods.The Pb substitution rate of CsPb_xMn_1-xCl₃ NCs can be as high as 46%,and the PLQYs can be 54%.The enhanced emission is attributed to the energy transfer of photoinduced excitons from the CsPbCl₃ host to the doped Mn,which facilitates exciton recombination via a radiative pathway.The intensity and position of this Mn-related emission are also tunable by altering the experimental parameters,facilitating synthesis and fluorescence adjustment of a series of low toxic PNCs.In the fourth chapter,in order to improve the water stability of PNCs,the NH₂-PEG-COOH was used as the ligand to passivate PNCs and assisted with Mn doping to reduce the content of lead.CsPb_xMn_1-xCl₃/NH₂-PEG-COOH with high PLQYs,water stability and low toxicity were synthesized.Due to the ligand-passivation effect of NH₂-PEG-COOH,the PLQYs of the PNCs aqueous solution is as high as 65%and the aqueous solution still retains the PLQYs of 30%after being preserved for 60 days.The experimental results show that the prepared NCs have low cytotoxicity and high PLQYs,and it has been applied to fluorescent probes for cell imaging,and demonstrated good fluorescence imaging capabilities.