Full-Color Light-Emitting Carbon Dots with a Surface-State-Controlled Luminescence Mechanism

Abstract

Carbon dots (CDs) with tunable photoluminescence (PL) and a quantum yield of up to 35% in water were hydrothermally synthesized in one pot and separated via silica column chromatography. These separated CDs emitted bright and stable luminescence in gradient colors from blue to red under a single-wavelength UV light. They exhibited high optical uniformity; that is, every sample showed only one peak in the PL excitation spectrum, only one peak in the excitation-independent PL emission spectrum, and similar monoexponential fluorescence lifetimes. Although these samples had similar distributions of particle size and graphite structure in their carbon cores, the surface state gradually varied among the samples, especially the degree of oxidation. Therefore, the observed red shift in their emission peaks from 440 to 625 nm was ascribed to a gradual reduction in their band gaps with the increasing incorporation of oxygen species into their surface structures. These energy bands were found to depend on the surface groups and structures but not on the particle size, not as in traditional semiconductor quantum dots. In addition, because of their excellent PL properties and low cytotoxicity, these CDs could be used to image cells in different colors under a single-wavelength light source, and the red-emitting CDs could be used to image live mice because of the strong penetration capability of their fluorescence.

Production of yellow-emitting carbon quantum dots from fullerene carbon soot

“…The emission wavelength first moves to higher values when the pH is increased from 2 to 8, then decreases with a further increase in the pH. Similar trend has also been reported previously [23,24,45,[54][55][56], which could be caused by the change of surface charge density induced by the protonation-deprotonation processes.…”

“…CQDs emit blue light, with an exception of a few studies reporting longer wavelength emissions (such as the emission of red light) [31,[43][44][45]. Interestingly, the main product of the CQDs (sample IV) could emit yellow light, as evidenced from Fig.…”

Hydrothermal Synthesis of Photoluminescent Nanocarbon from Hydroxylic Acids and Amines

“…The spectral changes of the PL emission suggests that the formation 6 of carbogenic core which is considered to give emission at longer wavelengths [21]. Because careful fractionation of the CDs by their different surface polarities gives several distinct absorption bands in visible light region [24], the red shift may be caused by the surface modification of the CDs. For the methylated EDAs (DMEDA and TMEDA), the intensity of the absorption band at ~330 nm becomes substantially smaller than those from EDA as shown in Figure 3.…”

Carbon Quantum Dots: A Safe Tool to Learn about Quantum Phenomenon in Nanomaterials

“…During this process, spontaneous emission of radiation can be observed as a way to discard the excess of the energy to stabilize the quantum system. Besides this basic chemistry, the instructor may briefly cite other photoluminescence mechanisms related to the band gap transitions between π-domains or defects on the surface of CQDs [45][46][47]. The fact of the photoluminescence mechanism remains unclear can further lead the students to understand chemistry as a building science.…”