Photoluminescence and solid-state LED application based on pH-sensitive carbon quantum dots

Carbon quantum dots (CQDs) have attracted great interest on account of their outstanding physicochemical properties. Herein we study the optical properties of the CQDs (diamond structure) and observe interesting phenomenon of concurrent multiband luminescence across the whole visible region. What is more, the CQDs exhibit emission-dependent excitation and high pH-sensitive. The surface structural and luminescence investigation in conjunction with density functional theory calculation reveal that C(O)O, C(O)NH2, and C(O)OH-related surface defects in these CQDs lead to observed luminescence. The calculation shows that stronger transitions between band edges of C(O)NH2-terminated CQDs leads to relatively strong photoluminescence in strong contrast with usually weak emission in oxygen terminated CQDs. Finally, the solid-state LED devices with different emission colors were fabricated based on the pH-sensitive properties of the CQDs.