Understanding and engineering the photophysics of single CdSe nanocrystals

Abstract

This thesis focuses on uncovering the photophysics of CdSe semiconductor quantum dots (QDs) at the single QD level, and correlating the phenomenological behavior observed at the single QD level to that observed at the ensemble level. Understanding the photophysics of QDs can potentially allow the specific optical properties of QDs to be applied in various ways. For example, through the study of the emission polarization of single QDs a 2D transition polarization property was discovered at room temperature. This enables us to monitor the 3D orientational dynamics of a target system by rigidly attaching a single QD to the system. Semiconductor QDs offer many advantages over other chromophores in a variety of applications because of their relatively narrow emission line width, an absorption spectrum that is well suited for multiplexed fluorescence detection, and their optical stability. However, fluorescence blinking phenomena in single colloidal QDs have been largely regarded as a undesirable optical properties. We have began to understand the phenomenology of the fluorescence blinking through a study of the statistics that are embedded in the fluorescence intensity time traces of collection of QDs. We have developed a statistical description of fluorescence blinking of single QDs and connected the blinking statistics to the fluorescence time traces of a collection of QDs. This study has shown that the fluorescence behavior of a collection of QDs is ergodic and moreover that it contains all the statistical information observed at the single QD level.