Optical Properties of Colloidal II-VI and III-V Semiconductor Nanocrystals: Single Nanocrystal Photon Correlation Spectroscopy

Abstract

Colloidal nanocrystals (NCs), also known as quantum dots, are nanometer-sized semiconductor crystalline structures comprised of thousands to tens of thousands of atoms placing them in a world between the molecular-sized and the bulk-sized world, allowing them to harness unique qualities from both. Colloidal NCs are used in many applications including light-emitting diodes (LEDs), photovoltaics (solar cells), lasers, transistors, photocatalysis, and many more. In this thesis, I investigate the optical properties of colloidal NCs, specifically InP/ZnSe/ZnS, CdSe/CdS/ZnS, and ZnSe/ZnS NCs using a combination of ensemble and single NC photon correlation spectroscopic techniques. In the first chapter, I introduce the photophysical properties of colloidal NCs and spectroscopic techniques relevant to my studies. In the second chapter, I determine the dominant photoluminescent line shape broadening mechanisms in single InP/ZnSe/ZnS and CdSe/CdS/ZnS NCs using temperature dependent photoluminescent spectroscopic techniques. In the third chapter, I investigate the coherent emissive properties of single InP/ZnSe/ZnS and CdSe/CdS/ZnS at cryogenic temperatures, demonstrating the longest coherence time measured in a colloidal NC system to date. In the fourth chapter, I develop an ensemble third-order correlation technique to elucidate the average single ZnSe/ZnS NC triexciton efficiency and dynamics. Finally, I propose future directions in the fifth chapter, including a fourth order correlation technique to resolve absolute energy information on timescales faster than CCDbase spectroscopic techniques, and an open-access photon correlation Monte Carlo toolkit with the aim of filling education gaps and provide the colloidal NC community with a database of analytical tools that will encourage a wider audience to engage with photon correlation spectroscopy.