Date of Award

1-1-2012

Document Type

Campus Access Thesis

Department

Chemistry and Biochemistry

Sub-Department

Chemistry

First Advisor

Mark A Berg

Second Advisor

Hui Wang

Abstract

CdSe-ZnS core-shell quantum dot relaxation dynamics are multiexponential and have a strong power dependence. Because single exciton and biexciton populations, are indistinguishable by any-dimensional experiments, there is uncertainty as to whether this power dependence comes from a biexciton or a photo-induced byproduct. Multiple population period transient spectroscopy, (MUPPETS), is a new two-dimensional spectroscopic technique that uses decay-rate variation to investigate heterogeneity in multiexponential processes. In this paper stat dependent behavior is used to isolate and identify the biexciton. The 2D MUPPETS signal shows a rise below 100 ps, and one-dimensional MUPPETS and pump-probe signals do not. A photo-induced byproduct would not explain the rise feature. This early time feature is power dependent. A least squares fit linear regression performed on the measured relaxation curves at each time across the different powers gave two terms, one power independent term and one power dependent term. The power independent terms are the low power limit of a relaxation and are shown to match power independent pump-probe data. The power dependent terms are all of the power dependent components and are shown to match the signal difference between the one-dimensional and two-dimensional MUPPETS measurements below 100 ps. Two-dimensional MUPPETS analysis separates the biexciton and single exciton, and the matches with empirical data confirm their identities. With further analysis, fits that match one-dimensional and two-dimensional data will provide characteristics describing the components, determine the number of components, and identify the behavior of the individual components in each population's dynamics. With successful fits, it can be determined if there is a correlation between the single exciton and biexciton dynamics. Deeper understanding of exciton and biexciton dynamics will help in the synthesis and development of solar cells and other energy harvesting devices.

Rights

© 2012, David Christopher Phillips

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