Date of Graduation

5-2014

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Chemistry (PhD)

Degree Level

Graduate

Department

Chemistry & Biochemistry

Advisor/Mentor

Heyes, Colin D.

Committee Member

Adams, Paul D.

Second Committee Member

Chen, Jingyi

Third Committee Member

Wang, Feng

Keywords

CdTe Quantum Dots; Coordination of Ligands; Core/shell/Shell; Interfacial Chemistry; Quantum Yields; Radiative and Nonradiative Lifetimes and Rates

Abstract

Colloidal semiconductor nanocrystals (quantum dots) have received a great deal of attention due to their superior size tunable properties and promising applications in many areas. Some of the most practical areas of their applications include light emitting diodes (LED), photovoltaic and biological studies. Synthetic methods of these crystals is becoming more established with new strategies being reported every now and then. However, quantitative studies connecting the processes at the interface, namely core-ligand, core-shell and shell-shells, to the overall quantum dots fluorescence properties are not well understood. Specifically for cores, relating surface-atoms interactions, solvents, ligands nature, density and functional groups on quantum yields have not been exhaustively carried out. Furthermore, for the core/shell counterparts, the connection between the qualities of the starting core on its resulting core/shell quality have been left trivial without experimental back up. Here, we summarize the reports of experiments that have systematically investigated these effects on the properties of quantum dots. Combining systematic synthetic approach with characterization tools such as FTIR, X-ray photoelectron and diffraction together with time resolved visible spectroscopies, we observed that the density, nature and the orientation of the ligand functional groups play significant roles in determining the charge carrier dynamics that results on the various quantum yields and quality of the quantum dots. The experimental results also contradicted the trivial belief that starting with a high quality core material should result into high quality core/shell quantum dots. We further extended these studies by controlling both lattice mismatch and exciton confinement potential to design small, biologically friendly and highly stable core/shell/shell material. Blinking studies confirmed an interplay of both lattice strain and exciton confinement as the major factors responsible for the blinking dynamics of these core/shell/shell quantum dots. Therefore, by controlling these parameters, we were able to observe

reduced blinking quantum dots with relatively moderate shell thickness. These observations will provide a useful insight while designing these particles and enhance their future applications.

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