Date of Graduation

5-2023

Document Type

Thesis

Degree Name

Bachelor of Science in Physics

Degree Level

Undergraduate

Department

Physics

Advisor/Mentor

Heyes, Colin

Committee Member/Reader

Churchill, Hugh

Committee Member/Second Reader

Wang, Yong

Committee Member/Third Reader

Aloia, Lindsey

Abstract

Under continuous excitation, quantum dots exhibit random transitions between fluorescent ON states and non-fluorescent OFF states --- a phenomenon known as blinking. A physical description of the mechanism responsible for blinking that applies broadly to many types of quantum dots remains under debate. We study the blinking behavior of the non-toxic CuInS2 quantum dot, a system that has seen little investigation at the single-particle level. In particular, the optical properties of CuInS2 quantum are often improved by adding ZnS to the nanoparticles, but this addition leads to complex structural-optical property relationships that are even less understood. To probe the relationship between quantum dot structure and blinking, we synthesize CuInS2 with ZnS using two different alloying methods and record their single-particle fluorescence intensity. The resulting particles have been shown to differ in their distribution of zinc. One set exhibits a radial gradient distribution as a result of cation exchange during core/shell formation while the other is a homogeneous alloy of Cu, Zn, In, and S. CuInS2/ZnS quantum dots with a gradient distribution of zinc exhibit suppressed but heterogeneous blinking, whereas quantum dots with a homogenous distribution of zinc exhibit higher but more uniform blinking behavior. An unexpected power dependence is observed in the OFF state dwell times in both samples, and a model of the mechanism producing this dependence is proposed.

Keywords

quantum dot; blinking; fluorescence intermittency; excitation power; alloying; non-toxic

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