Efficient synthesis of carbon dots with high aqueous quantum yield for achieving sustainable and gentle illumination

Luminescence from the sp 2 -conjugated carbon core of carbon dots (CDs) has long been regarded as their intrinsic bandgap emission, but building a clear scientific link between them remains a challenge. This pursuit is key because the solvent relaxation of water molecules is highly quenchable for CDs, strictly limiting whose aqueous solutions from generating the strong and stable emission. Herein, a facile solvent-free thermal dehydration process at ambient pressure is developed to yield CDs, in which sodium lignosulfonate directs the formation of the sp 2 cores covalently bridge to the non-extended conjugation that hinders π - π stacking. Combined with their highly conjugated structure that is tolerable to water quenching, vivid cyan fluorescence is easily obtained with the high aqueous quantum yield of up to 80.6%. A light emitting diode is further built by largely replacing the commercial phosphor by the CDs, high color rendering index of 88.2 and luminous efficiency of 58.3 lm W −1 can be obtained at a rather low input (20 mA). Moreover, its Commission Internationale de L’Eclairage 1931 color coordinates of (0.34, 0.35) are close to the ideal light source, jointly promising this study with considerable application significance.