Concentration-induced multi-colored emissions in carbon dots: origination from triple fluorescent centers.

Color-tunable carbon dots have been synthesized via a one pot hydrothermal synthesis and re-dispersed in dimethylformamide solution after purification. Structural and optical property characterizations indicate that the concentration-dependent photoluminescent properties can be ascribed to the existence of multi-emissive centers in the carbon dots from core states, edge states and surface states. Therefore, a multi-center fluorescent mechanism for the carbon dots has been proposed according to the preservation effect and inductive effect of the solvent. The emission wavelength of the carbon dots with different concentrations can be tuned from 585 to 514 nm under the fixed excitation of 420 nm blue light, and a warm white light-emitting diode with a CIE color coordinate at (0.42, 0.35) is fabricated on a InGaN blue chip emitting 420 nm blue light.