Confocal Microscopy Studies of Fluorescence Blinking of Semiconductor Quantum Dots, Metal Nanoparticle Photogeneration, and Multiphoton Photoemission from Thin Metal Films and Metal Nanoparticles

Since the advent of single molecule spectroscopy in 1989, advances in the field have revealed a wealth of information on dynamics and sample heterogeneity unobtainable by traditional ensemble studies. Microscopy experiments are a common technique to characterize and probe single molecule dynamics, due to the combination of the diffraction limited spatial resolution and the availability of sensitive single photon/electron detectors. Additionally, high excitation power densities can be achieved by the use of large numerical aperture objectives with moderately intense light sources. Fluorescence intermittency, or blinking, is a unique property found in the emission of single molecules. A series of experiments are undertaken to elucidate contributions to the blinking dynamics in nanocrystal semiconductors, or quantum dots (QDs). Investigations of the transitions from “on” to “off” (and vice versa) in the absence of laser illumination allow for the determination of the roles of light versus non-light induced processes for single blinking QDs. Small molecules are found to influence QD blinking by altering the surface trap state distribution due to changes in the electrochemical potential of the solution. However, fluorescence detection is only one implementation to investigate single molecule systems by microscopy. Nanoscale metal materials possess many interesting electronic and optical properties that enable single molecule or particle detection. Silver and gold metal nanoparticles are of particular interest due to their surface plasmon resonances (SPRs), a