Exciton Photophysics at Fluorescent Quantum Defects
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Fluorescent quantum defect is an emerging synthetic structure that can be covalently attached to a semiconducting single-walled carbon nanotube. Incorporation of fluorescent quantum defect breaks the symmetry of carbon nanotubes at a defect center, creating new optically allowed, low-lying states in the electronic structure of carbon nanotube. Exciting electronic and optical properties arise from the defects, including the generation of new photoluminescence features, which can be used for applications, such as chemical sensing, bioimaging, and quantum light source. As excitons dominate the optical properties of carbon nanotubes, understanding the exciton photophysics in a defect-tailored carbon nanotube is essential to efficiently harness the emission properties of fluorescent quantum defects. In this dissertation, I aim to understand the exciton photophysics in fluorescent quantum defects in order to explain the origins and behavior of novel phenomena arising from them. First, the structure-property relationships of fluorescent quantum defects are discussed; these guide the systematic tuning of defect-induced emission and the binding energy of defect-trapped excitons. Then, the discussion moves to the exciton dynamics at fluorescent quantum defects. Particularly, I describe how the chemical nature of defects or the density of defects influences the thermal detrapping energy of excitons. The exciton-electron interaction at a fluorescent defect is also discussed. Our results suggest that a fluorescent quantum defect colocalizes an exciton and an electron as a tri-charge carrier and the brightening at the defect can be chemically tuned. Finally, I introduce super-resolved, hyperspectral photoluminescence spectroscopy, enabling both direct probing of a single fluorescent defect and the quantitative evaluation of the brightening of dark excitons.