Recently, owing to the high stability and biocompatibility, carbon dots, especially sp2-bonded graphene quantum dots (GQDs), become new-generation photoluminescence materials, and have the potential for replacing commonly used fluorescent dyes and semiconducting quantum dots. [1,2] Nevertheless, the application of GQDs is still limited because of the relatively low quantum yield and limited wavelength. Tremendous efforts have been made to synthetic GQDs and other carbon dots with high quantum yields, such as surface passivation and chemical modification.[3] So far, the highest quantum yield is 0.62 for surface-modified carbon dots and 0.49 for surface-passivated GQDs, respectively. It is still much lower than that of fluorescent dyes or semiconductor quantum dots. What's more, the photoluminescence mechanism of GQDs is complicated and controversial. It is still unclear how to improve of quantum yield since size effect, defects and surface modification etc. were reported to be key factors for photoluminescence of GQDs. we report the synthesis of 1-3 nm N doped GQDs (N-GQDs) with higher quantum yield (0.74) than some fluorescent dyes via cutting graphene oxide and in situ doping progress without further surface passivation or modification. The key factor that affects the photoluminescence intensity was experimentally demonstrated to be the n-π* transition between the N in aromatic ring and conjugate structure of graphene. The strong fluorescence in solid state, good stability, excellent anti-jamming performance, as well as biolabeling agent for HeLa cells, confirm the advantages over the traditional fluorescent dyes. We will further present newest results on the photoluminescence wavelength control and usage of GQDs on the aqueous dispersion of graphene powders.

Recently, owing to the high stability and biocompatibility, carbon dots, especially sp2-bonded graphene quantum dots (GQDs), become new-generation photoluminescence materials, and have the potential for replacing commonly used fluorescent dyes and semiconducting quantum dots. [1,2] Nevertheless, the application of GQDs is still limited because of the relatively low quantum yield and limited wavelength. Tremendous efforts have been made to synthetic GQDs and other carbon dots with high quantum yields, such as surface passivation and chemical modification.[3] So far, the highest quantum yield is 0.62 for surface-modified carbon dots and 0.49 for surface-passivated GQDs, respectively. It is still much lower than that of fluorescent dyes or semiconductor quantum dots. What's more, the photoluminescence mechanism of GQDs is complicated and controversial. It is still unclear how to improve of quantum yield since size effect, defects and surface modification etc. were reported to be key factors for photoluminescence of GQDs. we report the synthesis of 1-3 nm N doped GQDs (N-GQDs) with higher quantum yield (0.74) than some fluorescent dyes via cutting graphene oxide and in situ doping progress without further surface passivation or modification. The key factor that affects the photoluminescence intensity was experimentally demonstrated to be the n-π* transition between the N in aromatic ring and conjugate structure of graphene. The strong fluorescence in solid state, good stability, excellent anti-jamming performance, as well as biolabeling agent for HeLa cells, confirm the advantages over the traditional fluorescent dyes. We will further present newest results on the photoluminescence wavelength control and usage of GQDs on the aqueous dispersion of graphene powders.