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Study on CdSe/ZnS (Core/Shell) Quantum Dots and the Emission-Absorption Spectra of the Quantum Dots Doped in Pmma

Author: WuZiQi
Tutor: ChengCheng
School: Zhejiang University of Technology
Course: Optics
Keywords: CdSe/ZnS quantum dot (CdSe/ZnS)/PMMA PL peakintensity PL peak wavelength red shift
CLC: O471.1
Type: Master's thesis
Year: 2013
Downloads: 3
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Abstract


Plastic optical fibers receive much attention due to its advantages of low prices, good flexibility, and easy connection although conventional glass fibers have been used widely in all-optical network communication systems. Plastics (for example, Polymethylmethacrylate (PMMA)) can be directly drawn into the fibers with desirable lengths and diameters by using current drawing techniques. In spite of the stable optical property, however, the plastic fibers have large absorption losses due to low transparency. Therefore, a new type of plastic fibers with low loss, widen bandwidth, high gain and desirable optical property is very needed for telecommunications and the other photoelectronic devices.In recent years, CdSe quantum dot (QD) has received much attention due to its strong fluorescence, visible wavelength, simple synthesis technique, and stable optical property. Therefore, it is interesting whether we can construct a quantum dot doped amplifier using the CdSe QDs as the gain medium to obtain high flatten gain and low noise.In this dissertation, the CdSe QD dispersed in N-hexane was fabricated by Organo metallic method in laboratory. The spectrum measurement shows that such QDs in the diameter of5.6nm possess the emission peak of625nm and the absorption peak of615nm (the Stokes shift of10nm).In this dissertation,(CdSe/ZnS)/PMMA QD doped fiber material is prepared by adding CdSe/ZnS (core/shell) QDs into the PMMA. The absorption-emission spectra and the refractive index of the (CdSe/ZnS)/PMMA are measured in respect with doping concentrations, and compared with the case of the QDs dissolved in n-hexane. It is shown that the absorption-emission peak wavelengths of the (CdSe/ZnS)/PMMA are identical with that of CdSe/ZnS. In the doping concentration ranging (0.013～0.130) mg.mL-1, the observed photoluminescence (PL) peak intensity shows a single peak following an exponential square law. As the doping concentration increases, the refractive index increases0.0013at room temperature, and the PL peak wavelength appears a red shift. The maximum red shift is limited by the Stokes shift, likely to be related with re-absorption/excitation effect and concentration effect of QDs. In addition, three different methods of drawing (CdSe/ZnS)/PMMA into the plastic fiber are designed and tried in experiment. Unfortunately, the results are unsatisfactory according to such methods. The reasons are summarized and in the end of this dissertation.

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CLC: > Mathematical sciences and chemical > Physics > Semiconductor physics > Semiconductive Theory > Semiconductor quantum theory
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