Session: Advances in Spectroscopy:

Semiconductor quantum dots (QDs) have generated substantial research interest in the past two decades because of their connection to various applications such as cancer treatments, photovoltaics, bio-labeling, and fluorescence microscopy. Specifically, cadmium-containing luminescent quantum dots (QD) are being widely used because of their relatively simple synthesis and enhanced photophysical properties. However, there is significant concern about the impact that cadmium-containing luminescent QDs can have on natural systems and human health as they degrade i.e., “weather” in the environment. Real-time monitoring of QD degradation and interaction with environmental systems is a valuable tool in understanding the factors that impact QD weathering. Previous work by others has demonstrated that combining time-resolved fluorescence measurements with quantum yield determinations and peak width determinations provides valuable information regarding semiconductor QD as they grow and degrade. However, the use of single-channel, time-resolved fluorescence measurements provided limited utility as a stand-alone analytical technique for quantum dots because the spectral response to simultaneous changes in QD properties can produce ambiguous spectral results.

In this research, multichannel, broadband, frequency-domain dynamic fluorescence measurements are used to monitor the progress of selected steps in the synthesis of ZnS passivated CdTe semiconductor quantum dots capped with mercaptopropionic acid (MPA) ligands. Monitoring QD processes using wavelength- and frequency-resolved fluorescence decay measurements produces Fourier-transform emission-decay matrices (FT-EDMs), which can be analyzed numerically for the spectra, decay rates, and relative intensities of the fluorescent sample components with minimal a priori assumptions. Surface passivation of CdTe quantum dots has been observed to have an appreciable impact on the QD fluorescence lifetime, so FT-EDMs collected after ZnS surface passivation will reflect changes in QD spectral properties. The spectra, decays and relative intensities of fluorescent components resolved from FT-EDMs collected as CdTe QDs react with ZnCl₂and MPA in HPLC grade water at 95^○ C will be described. Fluorescent components that change during the course of the reaction will be correlated to the modification of the QD surface.

Sharon Neal

Appearances