A facile and green method to tailor surface groups of carbon quantum dots (CQDs) is developed by hydrothermal treatment in an autoclave. The photoluminescence (PL) behaviors of CQDs depend on the types of surface groups. Highly efficient photoluminescence is obtained through amino-hydrothermal treatment of the CQDs reduced by NaBH4. The effects of surface groups on PL behavior are attributed to the degrees of energy band bending induced by surface groups. (C) 2014 Elsevier B.V. All rights reserved.