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Preparation and Photoluminescent Characteristics of ZnS and Doped ZnS Quantum Dots

Author: DongDongQing
Tutor: LiZuo；ZhangXiaoSong
School: Tianjin University of Technology
Course: Condensed Matter Physics
Keywords: ZnS Quantum dots Fluorescence Aqueous coprecipitation Hydrothermal Liquid - solid - solution method
CLC: TN304
Type: Master's thesis
Year: 2008
Downloads: 820
Quote: 2
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Abstract

In recent years, semiconductor quantum dots due to its unique nature more and more people's attention, has become an emerging cross-disciplinary, whose research in physics, chemistry, materials, biology and other disciplines, research priorities are from the original quantum Point Preparation and transferred to the basic properties of functional applications. Fluorescence is an important feature of quantum dots, ten years has been a research focus. This thesis doped zinc sulfide and zinc sulfide quantum dots preparation and spectral properties to carry out research, the main research contents and results are as follows: (1) using aqueous coprecipitation ZnS quantum dots, X-ray diffraction analysis and transmission electron microscopy tests shows that the sample sphalerite structure, diameter 3 ^{4 nm spherical ZnS particles. Fluorescence test found that with excitation peak wavelengths from 330nm to 380nm, emission spectrum of the sample maximum at 485nm from 430nm to move, luminous color from blue to white. Emission spectrum by a Gaussian fitting showed peaks at 416nm, 460nm and 505nm superposition of three peaks. The fluorescence spectra, absorption of 330nm light surface states after capturing part of radiative transition back photoelectron valence band and hole recombination, issued about 416nm blue-violet light; another part of the way of a non-radiative relaxation S2-vacancy trap levels are captured , and then to the valence band and Zn ^{2 vacancy defect level, respectively, with the wavelength of 460nm and 505 nm light. S2-vacancy is generated from the light absorption around 380nm 460nm and 505 nm emission. For surface having an organic ligand molecule chains, ZnS quantum dots, blue light is not found, this is because the organic molecular chain effectively modified surface state of the samples, the surface state of light disappears. (2), respectively, compared with water precipitation method, hydrothermal method and liquid - solid - solution was prepared by three different particle sizes ZnS: Mn ^{2 quantum dots. Testing found that particles with quantum dots increases, ZnS substrates and Mn ^{2 position of the excitation peak separation is more prominent. We believe that Mn ^{2 and ZnS substrates does not exist between the energy transfer process. Changing the molar ratio of precursor found with [S2-] / [Zn ^{2 ] ratio increases, the substrate emission peaks disappear and Mn ^{2 luminescence enhancement, because excess S2-adsorbed on the sample surface and the Mn ^{2 , after the formation of MnS thin layer coated on the surface of the sample, on the one hand, reducing the surface defects, the defect state ZnS substrate surface emission related decline; another aspects, but also modification of the surface of the non-radiative transition channel, so that the excitation energy as much as possible by Mn ^{2 absorption, resulting in Mn ^{2 luminescence enhancement. (3) water phase coprecipitation of Cu ^{2 doping and Cu ^{2 , M (M = F-or Ce3) co-doped ZnS quantum dots. Discussed the ZnS: Cu ^{2 quantum dot fluorescence emission mechanism, Cu ^{2 doping concentration and the incorporation of F-and Ce3 fluorescence spectra of the sample. Spectral tests found ZnS: Cu quantum dot emission peaks at 460nm and 490nm, respectively, at. These two peaks are from the matrix deep donor and shallow donor level and Cu ions t electronic transitions between energy levels caused by emissions. F-sensitizing as Cu ions substitute S2-forming positively charged center FS *, it may lead to the excitation energy and F-FS * no radiation transfer occurs between the fluorescence weakened. Coactivator Ce3 replacement lattice Zn ^{2 , at the bottom of the conduction band bottom center of the formation of positively charged, negatively charged form of Cu center to form a donor - acceptor pair, so that luminescence enhancement. (4) were prepared by two kinds of Pb ^{2 adsorption and Pb ^{2 -doped ZnS quantum dots. Found that the emission spectra of the two samples by a peak at 460nm and 520nm superposition of two peaks, they were derived from the Pb ^{2 Internal 3P1 → 1S0 and 1P1 → 1S0 transition launch. Explores the doping concentration, the precursor molar concentration ratio and surface modification on the fluorescence properties of the sample, the fluorescence detected Pb ^{2 optimal doping concentration of 0.3 at%; With precursor molar ratio increasing redshift sample emission peaks.}}}}}}}}}}}}}}}}}}}

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