The Emerging Development of Multicolor Carbon Dots

Abstract

single-layer graphene or a sheet of graphene consisting of a few atomic layers. As the graphitic fragment, GQDs exhibit reserved graphitic domains (sp 2 domains). Additionally, they are usually anisotropic and have obvious and similar graphitic lattice and chemical groups in the edge or interlayer defects. The morphology of CQDs is quasi-spherical carbonic nanoparticles, and its surface has obvious lattice and chemical groups, showing the intrinsic state luminescence and quantum confinement effect of the size of CQDs. It is believed that they have crystalline core based on sp 2 and sp 3 domains mixtures. The wavelength of PL can be adjusted by adjusting the size of CQDs. CNDs have a high degree of carbonization, with some chemical groups on the surface, but usually have no obvious lattice structure and polymer characteristics. PL mainly comes from the defects/surface states and sub domain states in the graphite carbon core, without the quantum confinement effect of particle size. Therefore, CNDs are defined as quasi-spherical carbon nanoparticles (CNPs) which are mainly composed of amorphous structural core. CPDs have a polymer/carbon hybrid structure via the aggregation or crosslinking of linear polymers or monomers, which are composed of rich functional groups/polymer chains and carbon cores on the surface. CPDs not only have the excellent optical properties of traditional carbonized CDs, but also succeed the properties of polymers. Yang et al. [3] considered that the carbon cores of CPDs include several subclasses: the complete carbonized carbon cores, the paracrystalline carbon structures consisting of tiny carbon clusters with polymer backbones, and highly dehydrated cross-linked and convoluted polymer frameworks. According to the review by Yang et al., [3] it shows that the emission of most CPDs is usually excitation-dependent and these emissions may originate from different fluorescence centers and complex energy levels. The luminescence of a carbon core with a perfect graphite structure can be generated by the intrinsic emission of the carbon core, and the energy band gap can be modified by the size of the carbon core. However, since CPDs are usually imperfectly conjugated and they have a polymer/carbon hybridized backbone structure, their luminescence mechanism is different from that of conventional CDs. However, the luminescence of CPDs is also affected by the size of the conjugated π-domain, which is considered as a subdomain, that is, the fluorescence centers within CPDs are called subdomain states. Thus, carbon core luminescence can also be obtained from the subdomain emission of the conjugated As a relatively new type of fluorescent carbon-based nanomaterials, multicolor carbon dots (MCDs) have attracted much attention because of their excellent biocompatibility, tunable photoluminescence (PL), high quantum yield, and unique electronic and physicochemical properties. The multicolor emission characteristics of carbon dots (CDs) obviously depend on the carbon source precursor, reaction conditions, and...

Blue, Yellow, and Red Carbon Dots from Aromatic Precursors for Light-Emitting Diodes

“…The tunable and multicolor PL property is so fascinating that researchers are making great efforts to synthesize, modify, and functionalize CDs in order to regulate and control the emission of CDs. The multicolor emission can be adjusted by the excitation of the wavelength, pH, the concentration, solvent used, carbon source, reaction condition, separation, and pressure [ 11 , 12 ]. Reaction conditions play a vital role in the synthesis of MCDs.…”

“…Reaction conditions play a vital role in the synthesis of MCDs. Reaction conditions include changing the response temperature [ 13 ], time [ 14 ], reactant ratio [ 11 ], reaction solvent type [ 15 , 16 ], and pH [ 17 ], or using machine learning assistance [ 18 ]. Among them, the reaction temperature influences the carbonization of carbon resources, then affects the degree of graphitization [ 1 , 13 ].…”

“…The reaction solvent will control the degree of carbonization and dehydration in the carbon precursors, and then affects the size of the sp 2 -conjugated domains [ 16 ]. The surface functional groups of CDs can be directly affected by the reactant ratio, affecting the surface energy levels and causing electron transfer [ 11 ]. Varying kinds of carbon precursors produce different CD carbon core hybridization and surface functional groups [ 12 ].…”

“…Varying kinds of carbon precursors produce different CD carbon core hybridization and surface functional groups [ 12 ]. The dispersion environments of MCDs, e.g., pH and solvents, cause a hydrogen bonding effect or π–π stacking interaction [ 11 , 12 ].…”

Evolution and fabrication of carbon dot-based room temperature phosphorescence materials

“…As a new class of the emerging carbon family of zero-dimensional fluorescent nanomaterial, CDs have attracted the widespread concern and the great research interest by a wide range of researchers owing to the distinguished properties such as adjustable photoluminescence (PL), excellent stability, facile surface functionalization, environmental friendliness, low toxicity and good biocompatibility. [2][3][4] According to the previous reports, 5 CDs can be classified into four types, namely carbon nanodots (CNDs), carbon quantum dots (CQDs), graphene quantum dots (GQDs) and carbonized polymer dots (CPDs). Specifically, GQDs are small graphene fragments less than 20 nm in lateral dimension and less than five graphene flakes (~ 2.5 nm) in height, exhibiting pre-existing graphitic domains (sp 2 domains) and edge-rich chemical groups.…”