Characterization of functionalized semiconductor quantum dots subjected to simulated weathering featuring wavelength- and frequency resolved photoluminescence decay measurements
Date
2023
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Publisher
University of Delaware
Abstract
Photoluminescent semiconductor quantum dots (QDs) have gain interest in the last twenty years because of their increasing use in diverse technologies, such as photodynamic therapy, solar cells, bio-imaging, sensitizers for radiotherapy, and radiation sensors. Particularly, cadmium-based luminescent quantum dots (QDs) are starting to be used in these technologies because of their easy synthesis and robust optical properties- which are found in the visible and near infrared regions- when compared to various types of QDs. However, the use of toxic heavy metal nanomaterials has generated concern about the effect that cadmium based luminescent QDs have on the environment and human well-being once they break down i.e., “weather”. This has contributed to the use of surface passivated cadmium-containing QDs and less toxic materials in order to enhance the QDs surface chemistries. Although many advances in the development of QD materials, structures, and surface chemistries have been made to increase the QDs physicochemical properties, there has been less attention given to investigating functionalized QD degradation as a function of the levels and types of radiation. ☐ The objective for this research contained in this dissertation is to investigate the progress of photo-induced weathering mechanisms of functionalized QDs using wavelength resolved frequency domain photoluminescence decay measurements, as well as characterize the impact of radiation based on the changes observed in the QDs’ emission using multivariate data analysis tools. This context is important because QDs and other nanomaterials are being rapidly integrated into existing and emerging technologies. Thus, this dissertation investigates the interactions of surface passivated CdSe/ZnS QDs with two types of radiation sources: simulated solar and ionizing radiation. We specifically monitored the weathering mechanisms induced by varying the level and type of radiation on the photoluminescence properties of CdSe/ZnS QDs capped with oleic acid (OA) ligands. Then, in the final chapter, the effect of simulated solar radiation on the optical properties of water soluble CdSe/ZnS QDs capped with dihydrolipoic acid (DHLA) ligands were monitored to investigate the impact of ligand type on the spectral components observed in the QDs emission. Various techniques, such as multichannel absorbance, steady state emission, dynamic photoluminescence measurements, transmission electron microscopy, dynamic light scattering, and numerical data analysis, were used to characterize changes in the components of the QDs’ luminescence. These studies have provided insight into the mechanisms that occur while the QDs are irradiated and new tools for characterizing the impact of radiation on materials for existing and new applications.
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Keywords
Cadmium containing, Multichannel photoluminescence, Quantum dots, Photoluminescence decay