Controllable Preparation And Property Investigation Of Functional Cadmium-free Quantum Dots

This thesis focuses on the preparation of functional multi-component cadmium(Cd)-free quantum dots,through the use of green and gentle aqueous synthesis.Magnetic metal elements were doped into quantum dots,and the influence of magnetic element doping on the optical properties of quantum dots were explored,in order to achieve an effective balance of optical properties and magnetic properties,and thus to realize the preparation of dual-functional quantum dots for better applications.On the other hand,by coating the ZnS shell layer,the fluorescence intensity and stability of the multi-component cadmium-free quantum dots were further enhanced.After the zinc sulfide shell layer was coated with organic sulfur source instead of inorganic sodium sulfide,which further improved the quantum yield.At the same time,the near-infrared emission was red-shifted.Combined with transient fluorescence spectra and surface analysis,the relevant photoluminescence enhancing mechanism was discussed in depth.Firstly,the quaternary CuInZnS quantum dots were synthesized by the aqueous phase method,and the fluorescence intensity was further enhanced by coating the ZnS shell.On this basis,the magnetic ion Mn²⁺was doped into ZnS during the shell formation process.By comparing the doping strategy and optimizing the doping molar ratio of Mn,the effects of magnetic Mn doping on the optical and magnetic properties of CIZS/ZnS core-shell quantum dots were systematically studied,and the optical and magnetic properties of quantum dots were effectively balanced.Secondly,a facile aqueous route was developed to prepare biocompatible ultra-small copper selenide nanoparticles,and the resulting nanoparticles showed high stability.On this basis,Cu Fe Se nanoparticles were prepared by doping Fe elements and optimizing the doping molar ratio of Fe.The doped nanoparticles were functionalized with dimercapto poly(ethylene glycol)(HS-PEG-SH).The experimental results showed that the obtained ultra-small Cu Fe Se nanoparticles showed wide near-infrared absorption,high photothermal conversion efficiency and ferromagnetism,which endow the nanoparticles the potential of application in simultaneous magnetic resonance imaging and photothermal therapy.Finally,in order to broaden the luminescence range of the multi-component Cd-free quantum dots in the near-infrared region,the Cu In Se/ZnS core-shell quantum dots were prepared by aqueous method.By studying the role of the sulfur source during coating ZnS shell,we found that using sulfur-containing organic compounds instead of inorganic Na₂S can improve the quantum yield of Cu In Se/ZnS quantum dots,and simultaneously achieve a red-shift of the near-infrared emission.Spectroscopy and structural characterization proved that in addition to acting as the sulfur precursor,the organic sulfur-containing compounds bearing coordinating groups contribute to reducing the surface defects as ligands,and thus enhance the PL.Its good fluorescence stability endows near-infrared emitting Cu In Se/ZnS quantum dots significant advantage in biological imaging.In general,this thesis provides a green and simple aqueous synthesis and optical/magnetic performance control strategy for achieving functional Cd-free quantum dots,which is of great significance to the practical application of quantum dots in the biomedical field.