▎ 摘　　要

A high concentration nitric acid oxidation strategy has been presented for one-step fabrication of strongly red-emitting fluorescent graphene quantum dots (GQDs) using activated carbon as a carbon source. In optimal conditions, the emission quantum yield at 600 nm wavelength is as high as 18%. The concentration of the used nitric acid is critical to the optical properties of the GQDs: concentrated nitric acid (14.6 M) can more sufficiently oxidize GQDs' surface and more efficiently dope the N element, resulting in a longer emission band and higher emission efficiency. Preliminary cell image study indicates the obtained GQDs possess a high signal to background ratio, good stability and low cytotoxicity, which endow their promise as a new type of near-infrared fluorophores for biological applications.