Controlled Aqueous Synthesis Of Doped Red- Emitting Quantum Dots And Its Application In LED

Compared with traditional incandescent lamps and fluorescent lamps,white LEDs have the advantages of low energy consumption,energy saving,long life,environmental friendliness and high color rendering index,and are calLED the fourth generation of green light source.Commercial method to achieve white light emission is to use blue chip to stimulate yellow phosphors.However,the color temperature of white light generated in this way is very high,and the color rendering index is low.This defect of commercial LEDs provides space for our research.As a new type of nanomaterial,quantum dots have smaller size,adjustable wavelength and better photothermal stability compared with traditional phosphors,so they have attracted increasing attention as candidate LED materials.Three kinds of doped red quantum dots:CdTe:Gd³⁺,ZnS:Mn and CuZnInS/ZnS were successfully prepared by aqueous phase method.In addition,the morphology,structure,luminescent properties of the three QDs were studied.Furthermore,they were combined with commercial blue light chip to produce white LEDs with high performance.In chapter 1,the luminescence mechanism,classification,synthesis method and application of quantum dots were briefly introduced,and the realization mode,advantages,status quo and prospects of the white light LEDs were also briefly introduced,which provided relevant basis for the research topic of this paper.In chapter 2,the instruments and chemical reagents involved in the preparation and characterization of samples were briefly introduced.In chapter 3,a series of color-tunable CdTe:Gd³⁺were prepared by aqueous phase heating method,and the luminescent properties of the prepared samples were studied.X-ray diffraction?XRD?results showed that the doping of Gd³⁺ions had no significant effect on the crystal structure of CdTe,which was attributed to zinc blende structure.Moreover,since the ion radius of Gd³⁺was smaller than that of Cd,the X-ray diffraction peak of CdTe shifted to the large angle direction,and the calculated particle size was about 3 nm,which was consistent with the transmission electron microscope?TEM?result.Photoluminescence?PL?spectrum and ultraviolet-visible?UV-Vis?absorption spectrum indicated that Gd³⁺ions lead to red-shift of the emission peak,and the absolute photoluminescence quantum yield?PL QY?of CdTe:Gd³⁺has been greatly improved to 85%after Gd³⁺doping.Through precipitation,centrifugation and drying,the powder of quantum dots was prepared.The optimal excitation wavelength of 460 nm matched well with the effective excitation of LED chip.In addition,the test results of WLED devices showed that CdTe:Gd³⁺quantum dot phosphor has a good application prospect.In chapter 4,a series of red phosphor ZnS:Mn²⁺were prepared by precipitation method.The crystal structure and luminescent properties were studied by XRD,excitation spectrum and emission spectrum.Among the obtained QD_S phosphors,the optimal doping concentration of Mn²⁺in the substrate ZnS was 5 mol%,and the optimal excitation peak was 460 nm,which was consistent with the emission wavelength of LED blue light chip.TEM showed that the particle size was about 5 nm,which was consistent with XRD data and had good monodispersity.The red light quantum dots were further applied to the preparation of WLED devices.In chapter 5,a series of color-tunable CuZnInS/ZnS were synthesized by aqeuous phase heating method.On the basis of the CuInS QDs,different proportions of Zn ions were doped to increase the fluorescence intensity and adjust the emission wavelength,and the fluorescence intensity and stability can be further enhanced by coating the ZnS shell.The crystal structure and luminescent properties were studied by XRD,excitation spectrum,emission spectrum,UV-Vis absorption spectrum and TEM.The CuZnInS/ZnS quantum dots are spherical with a particle size of about 3.5 nm,which was consistent with the particle size calculated by XRD.It can be seen from the fluorescence spectrum that the fluorescence intensity of quantum dots was greatly enhanced by the doping of Zn and the coating of ZnS shell.When Cu/Zn molar ratio was 1:1,the fluorescence emission peak was around 600 nm,and its corresponding strongest excitation peak was 460 nm,which was well matched with the emission of UV LED chip.The application of the quantum dot phosphors mentioned above in the preparation of white LED devices well complemented the lack of red light in commercial white LED,and the obtained device had a high color rendering index,indicating that the prepared doped quantum dots have promising application potential.