A facile and energy-efficient method is presented for the large-scale synthesis of fluorescent carbon dots whose fluorescence emission wavelengths shift gradually from 630 to 400 nm with reduction in their concentration.

To demonstrate the effects of surface atoms on photoluminescence (PL) and photocatalytic activities of luminescent carbon dots (CDs), we design and tailor the surface groups of CDs with heteroatoms by a facile and effective approach. The coexistence of O and N radicals in CDs results in strong PL while CDs containing O and Cl radicals show high photocatalytic activity. This is attributed to the different degrees and directions of energy band bending from inner to surface induced by O, N, and Cl radicals at the surface of CDs. The coexistence of both upward and downward band bending that are caused by the O and Cl radicals, respectively, in CDs is similar to an internal electronic field that facilitates the separation of electron–hole pairs and carrier migration, leading to high photocatalytic activity. These results may also be used for designing and tailoring optical–electronic properties of carbon nanostructures.