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Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Chemistry

Year Degree Awarded

2017

Month Degree Awarded

September

First Advisor

Kevin R. Kittilstved

Second Advisor

Michael D. Barnes

Third Advisor

Bret Jackson

Fourth Advisor

Anthony D. Dinsmore

Subject Categories

Inorganic Chemistry | Materials Chemistry | Nanoscience and Nanotechnology

Abstract

Semiconductor nanocrystal doping has stimulated broad interest for many applications including solar energy conversion, nanospintronics, and phosphors or optical labels. The study of the chemistry and physics of doped colloidal semiconductor nanocrystals has been dominated in the literature by isovalent dopants such as Mn2+ and Co2+ ions in II-VI semiconductors, in which the dopant oxidation state is the same as the cation ions. Until recently, aliovalent dopants has received much attention due to the plasmonic properties. Aliovalent is when the oxidation states of the dopant in the lattice differs from the cation ions. In the plasmonic semiconductor nanocrystals, the dopants are noted as the shallow donor and can donate electrons to the conduction band, resulting in the collectively resonate of the delocalized electrons under certain electromagnetic radiation, i.e. localized surface plasmon resonances (LSPR). However, only small amount of the dopants can donate delocalized electrons. The amount of ‘activated’ dopant is restricted by the synthetic methods and the defect chemistry related to the plasmonic property is still under debate. In this report, we are using Al3+ doped ZnO nanocrystals as an example. We have established a synthesis method to bring more dopant incorporation and less charge compensation defect, so higher electronically activated dopant is achieved. These results provide a synthetic strategy as well as the electronic structure understanding for the aliovalent dopants in semiconductor nanocrystals. On the other hand, less attention has been focused on the deep donor dopant such as Fe3+ in II-VI semiconductors. The deep donor, due to the oxidation redox potential lower than the conduction band potential (deep), instead of donating electrons in conduction bands, will donate electrons in trap states or defect states. For the deep donor, less is known for the driving force to determine the oxidation state of the n-type dopant. Here, we have developed a dopant-specific spectroscopy for estimation the deep donor Fe3+ speciation, i.e. substitutional, interstitial, or surface Fe3+ in ZnO nanocrystals and conducted photo-charging experiment to study the redox potential of the deep donor dopant. These studies could help to identify the dopant speciation and understand the interactions between the conduction band electrons and the deep dopants.

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