Synthesis and optical properties of nitrogen and sulfur co-doped graphene quantum dots

Strong blue luminescence and water-soluble nitrogen (N) and sulfur (S) co-doped graphene quantum dots (NS-GQDs) were fabricated via a one-step hydrothermal method using oxidized graphene. Ammonia and powdered S were selected as the source of N and S. respectively. The results indicated that both N and S atoms were successfully incorporated into the sp(2)-hybridized carbon framework of graphene. Under the excitation of 365 nm, the maximum emission intensity could be obtained with a 1:1.2 atomic ratio of N/S. The as-prepared NS-GQDs exhibited brighter luminescence compared with N-doped graphene quantum dots (N-GQDs). S-doping plays an important role in enhancing the emission intensity of NS-GQDs. In addition, the luminescence was exceptionally resistant to high salt concentration. Because of these virtues, there are extensive potential applications for NS-GQDs in bio-imaging, solar cells, and ion detection.