Realization of the Photostable Intrinsic Core Emission from Carbon Dots through Surface Deoxidation by Ultraviolet Irradiation

It is of a primary importance to realize the intrinsic emission from the inner carbogenic cores of carbon dots (CDs). In this work, CDs with three emission centers were synthesized by a microwave-assisted method using phloroglucinol as a precursor. The emission of these three centers has been identified as originating from molecular fluorophores, surface states of CDs, and the intrinsic CD core state. The emission from molecular fluorophores and from the surface state of CDs exhibited a weak photostability and could be photobleached as a result of UV laser irradiation. The emission from the intrinsic state of the inner carbogenic core has been found to be stable against photobleaching. On the basis of this difference in photostability, we demonstrate how the surface of CDs can be deoxidized under prolonged UV irradiation, resulting in a narrow intrinsic emission with a photoluminescence quantum yield of 17%.