Date of Award

8-2007

Degree Name

Master of Science

Department

Chemistry

First Advisor

Dr. Subra Muralidharan

Second Advisor

Dr. Sherine Obare

Third Advisor

Dr. Dongil Lee

Access Setting

Masters Thesis-Open Access

Abstract

The central theme of the research performed is the systematic modification of the optical properties of quantum dots by the formation of a shell of another quantum dot of a different band gap energy. Core/shell quantum dots such as CdS:Mn/CdS, CdS:Mn/ZnS, and ZnS:Mn/CdS with various concentrations of dopant Mn2+ in the core and shell concentrations have been synthesized under mild conditions in the aqueous phase using stoichiometric amounts of the surfactant stabilizer dodecyl sulfate. These quantum dots exhibit UV-vis, emission, and electron paramagnetic resonance (EPR) spectral behavior that is dependent on the concentration of the shell and the dopant Mn2+ in the core. The emission intensities of the core quantum dots do not exhibit a systematic variation with Mn2+ concentration. When a shell is added a systematic variation in the emission intensity and lifetime that are inversely proportional to the concentration of the shell is observed. When the large band gap ZnS is added as a shell to the small band gap CdS, the Mn2+ ions migrate from the core to the shell which is manifested in the emission and EPR spectra. Additionally the mixing of the valence and conduction band energy states of the large and small band gap shell and core respectively is also manifested in the emission spectra. In the reverse case, namely when CdS is added as a shell to ZnS the migration is not observed and the mixing of the valence and conduction band energy levels is minimum. The tunable optical properties of these core/shell quantum dots make them excellent platforms for the generation of nanosensors for nerve gas analogs.

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