| No matter in people’s life or industrial production, Carbon is very important. People think that carbon is black, solid mass, and very cheap. In fact, the luxurious and beautiful diamond is also made from carbon. In scientific research, carbon materials are very charming. Macroscopic carbon materials often lack the appropriate band gap, which are difficult to be developed as ideal fluorescent materials. However, when the size of the carbon materials achieved nanometer scale, typically less than 10 nm, will emit colorful lights and people call them carbon dots. Compared to traditional semiconductor quantum dots(QDs) and organic dyes, photoluminescent C-dots are superior in terms of high aqueous solubility, robust chemical inertness, easy functionalization, high resistance to photobleaching, low toxicity and good biocompatibility. As a result, much attention has also been paid to their potential applications in biological labeling, bioimaging, drug delivery, light energy conversion, photovoltaic devices and related applications. In this thesis, we use the hydrothermal method to prepare a series of fluorescent carbon dots with unique structures and outstanding properties by using the two amino acids of serine and tryptophan.In the second chapter, a fluorescent carbon dot with a cookie-with-chocolate film structure(about 5 × 5 μm2) showed a high fluorescence quantum yield(61.12%) at low p H. It was hydrothermally synthesized from L-serine and L-tryptophan. The formation mechanism of the film with carbon dots(CDs) was investigated. The film structure was formed by hydrogen bonding and π– π stacking interactions between aromatic rings. The strong blue fluorescence of the CDs increased under strong acidic conditions owing to the changes in the N-groups. These cookie-like CDs are attractive for their potential use as effective fluorescent probes for the sensitive detection of aqueous H+ and Fe3+. Then, we use a p H-dependent solubility equilibrium to develop a one-pot aqueous synthesis of polymer carbon nanodots with novel structures. The chemical structure and photoluminescence(PL) were heavily influenced by the synthesis p H, with polymer carbon nanosheets(3 < p H < 7), and amorphous carbon structures(1 < p H < 3) achieved by altering the initial p H. Although p H-dependent structures frequently occur in typical semiconductors and supramolecular architectures involving metal, this is the first experimental work describing it in carbon nanodots In addition, the photoluminescence quantum yield(PLQY) of the asprepared CNDs from either pure L-serine or pure L-tryptophan were independent of the synthesis p H, while the PLQYs of the CNDs made from a mixture clearly depended on the p H. The PLQYs of the L-serine/L-tryptophan CNDs made in acidic conditions were close to double those of CNDs similarly made in alkaline conditions. The only difference between L-serine and L-tryptophan is the hydroxyl and indolyl groups; therefore, in the acidic medium, the hydroxyl can oxidize L-tryptophan, which was the probable cause of the different reaction paths and the p H dependence of PL.In the chapter three, Carbon dots(CDs) were prepared with up to 89.57% PLQY, the highest yet reported. Their formation mechanism was systematically investigated by following the hydrothermal condensation of L-serine and L-tryptophan at different temperatures. At low p H, heating to 100 °C led to a CD molecular precursor with a weak PL spectrum and blue–green emission. At higher temperature(200 °C), a carbogenic core without lattice formed, and the quantum yield increased. At the highest tested temperature(300 °C), CDs with an obvious carbon lattice were obtained; they showed the highest absolute PLQY. Moreover, the carbon dots with obviously lattice show the room-temperature ferromagnetism. Theoretical calculation of the single layer of the carbon dots further explored the origin of room-temperature ferromagnetism in carbon dots. Then, we report a brand new theranostic nanomedicine(CDs-Cet) synthesized by means of the condensation reaction between the amino groups on the CD’s surface and the carboxyl group of Cetuximab. The new nanomedicine will help customize the injection time and dosage of the medicine. We believe that the development of highly biocompatible and fluorescent drug delivery systems based on fluorescent CDs holds great promise for specific drug delivery with minimal side effects and toxicity in cancer patients.In the chapter four, Supersmall carbon nanodots(SCNDs, ～0.5 nm) were obtained at p H < 1; their direct white emission can be easily applied as an inexpensive color-changing layer in white LEDs. Investigation of the PL mechanism of the SCNDs revealed an uncommon multilevel highly emissive recombination channel, which could be possibly derived from the wide distributions of surface-state PL centers. Theoretical calculation of the single layer of the carbon dots further explored Otheir band gap changes. We also analyzed the emission spectra of the SCNDs in the LED devices for their color emission. The CIE coordinates of(0.29, 0.31) show that these SCNDs are usefulas a single white-light phosphor for a white LED. In addition, the CRI and CCT are 81 and 6786 K, respectively. This represents a significant advancement in the applicability of CNDs. |
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