Green Synthesis of Carbon Dots toward Anti-Counterfeiting

The synthesis of carbon dots (CDs) from green precursors has received considerable attention recently. However, most of the natural biomass-derived products without further surface treatment usually have quite low quantum yield (QY) varying in the range of 2-30%. Herein, we report the sustainable fabrication of highly fluorescent CDs from food waste, turtle shells, and demonstrate their applications in the fields of multisignal coding and anti-counterfeiting with a combination of colloidal photonic crystals (CPCs). We utilized turtle shells as precursors to synthesize fluorescent CDs via a simple pyrolysis method. The resultant CDs without further surface treatment have an absolute photoluminescence (PL) QY of 45% and high dispersibility in various solvents. Then, we realized collective optical properties with a combination of CDs and CPCs, including diffractive light abilities and fluorescence. CPC/CD bead codes with a structural color and fluorescence were prepared via a microfluidic device. CPC/CD patterned films with PL and angular dependence of structural colors were also constructed via a 3D microfluidic printing technique, which are useful for multisignal anti-counterfeiting and various optoelectronic applications.