Study on the Origin of Fluorescence by Using Dual-Emission Carbon Dots

Fluorescent carbon dots (CDs) have attracted growing attention and have exhibited widespread potential applications in photocatalysis, bioimaging, and optoelectronics in recent years. However, due to the complex structure of CDs, both the molecular ingredients and the intrinsic mechanisms governing the fluorescence (FL) of CDs are poorly understood. Herein, dual-emission N-doped carbon dots (N-CDs) were synthesized through the solvothermal reaction of p-phenylenediamine and folic acid in deionized water. Interestingly enough, the second emission band of N-CDs can be tuned by changing the polarity of the solvent, showing an obvious solvent dependence. The first emission band has obvious excitation-wavelength dependence, while the second emission band does not. The first emission band likely comes from diversified amide units, while the homogeneous polymers chains are the most likely origin of the second emission band. These findings greatly improve our understanding of the FL origin of CDs and help to guide future preparations of novel nanomaterials.