Journal
NANO LETTERS
Volume 17, Issue 12, Pages 7710-7716Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.nanolett.7b03863
Keywords
Carbon dots; photoluminescence; fluorophore; polycyclic aromatic hydrocarbons; optical spectroscopy; electrophoresis
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Funding
- Bavarian State Ministry of Science, Research, and Arts through the grant Solar Technologies go Hybrid (SolTech)
- German Academic Exchange Service (DAAD) through a PPP Hong Kong grant [57320254]
- Germany/Hong Kong Joint Research Scheme - Research Grants Council of Hong Kong
- German Academic Exchange Service [G-CityU103/16]
- LMUexcellent Junior Researcher Fund
- Alexander von Humboldt foundation
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Carbon dots (CDs) are an intriguing fluorescent material; however, due to a plethora of synthesis techniques and precursor materials, there is still significant debate on their structure and the origin of their optical properties. The two most prevalent mechanisms to explain them are based on polycyclic aromatic hydrocarbon domains and small molecular fluorophores, for instance, citrazinic acid. Yet, how these form and whether they can exist simultaneously is still under study. To address this, we vary the hydrothermal synthesis time of CDs obtained from citric acid and ethylenediamine and show that in the initial phase molecular fluorophores, likely 2-pyridone derivatives, account for the blue luminescence of the dots. However, over time, while the overall size of the CDs does not change, aromatic domains form and grow, resulting in a second, faster decay channel at similar wavelengths and also creating additional lower energetic states. Electrophoresis provides further evidence that the ensemble of CDs consists of several subsets with different internal structure and surface charge. The understanding of the formation mechanism enables a control of the chemical origin of these emitters and the ensuing optical properties of the CDs through synthetic means.
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