On the Molecular Origin of the Red Emission in the Newly Synthesized Carbon‐Based Quantum Dots

Molecule or nanoparticle? A facile one-pot synthesis of red-emissive, carbon-based quantum dots is described using citric acid and formamide as precursors without addition of other nitrogen sources. A photophysical study of the system, including fluorescence correlation spectroscopic results, suggests that the carbon-based quantum dots, or at least their emissive centers, are not part of nanoparticles but rather resemble small organic fluorophores.

Abstract

Carbon-based quantum dots (QDs) represent a new family of luminescent nanomaterials with intriguing emission properties. They are synthesized predominately with the emission in the blue and green region of the visible spectrum, with limited success in producing red emission. Furthermore, the current literature on the subject lacks consensus with respect to the morphology of QDs. Contrary to their semiconductor counterparts, the data on the structure of fluorescing centers is scarce. Herein, we describe a facile one-pot synthesis of red emissive QDs using citric acid and formamide as precursors without addition of any other source of nitrogen. The photophysical properties of the synthesized species were investigated by steady state and transient absorption and fluorescence spectroscopy. Some structural peculiarities were revealed using fluorescence correlation spectroscopy. Our findings show that the newly synthesized carbon-based QDs, at least their emissive centers, are not part of nanoparticles but rather resemble small organic fluorophores. Furthermore, we have not eliminated the possibility that multiple fluorophores with different emission properties may be embedded within a single molecular entity.

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