Starch-Derived Carbon Dots with Enhanced Photoluminescence and Tunable Emission for Multilevel Anticounterfeiting

Carbohydrate-derived materials refashioned into carbon dots (CDs) are at the forefront of innovation for scalable carbon nanomaterial production and the sophisticated reclamation of biomass residues. Herein, we report an environmentally conscious synthesis of starch-based CDs, accomplished through a simplified, one-step method with a nitrogen-induced intramolecular charge transfer approach to bolster the CDs' photoluminescence quantum yields (PLQYs). Additionally, these starch-derived CDs exhibited a remarkable fluorescence (FL) blue shift and stimulus response of different excitations, spanning from a soft green to a deep blue. Detailed investigations of the characterization and energy level analysis revealed that the blue shift mechanism of CDs was attributable to the deliberate N doping. This process minimized the CD's size and elevated the optical band gap from 0.15 to 0.47 eV. An exemplary PLQY of 13.3% was attained for these CDs, representing a significant advancement compared to other carbohydrate-sourced CDs. The heightened graphite N composition is identified as the crucial element inducing the blue shift in FL emission. Crucially, with this distinctive capability for color modulation, starch-based CDs emerge as a potent tool for optical anticounterfeiting and intelligent information encryption.