Solvent-regulated synthesis of full-color fluorescent nitrogen/sulfur co-doped carbon quantum dots for anti-counterfeiting textiles

Carbon quantum dots (CQDs) have attracted widespread attention due to their unique optical, electronic,   and luminescence properties. However, synthesis   of highly-efficient panchromatic luminescent CQDs in aqueous solutions using non-benzenoid precursors remains a challenge. Herein, we proposed a simple one-step solvothermal strategy for developing full-color-emitting CQDs by the combined use of citric acid and thiourea. Through regulating the protonation extent of the solvent using water, glycerol and DMF, bright blue-, green-, yellow-, and red-emission CQDs were successfully synthetized, achieving the maximum emission wavelengths of 453, 531, 574 and 626 nm, respectively, and corresponds well to the calculated energy gap between HOMO and LUMO. Compared with those obtained from traditional methods, the fluorescence quantum yields of the prepared full-color CQDs were significantly increased by nitrogen-sulfur co-doping, reaching approximately 38.12 %, 32.50 %, 20.69 %, and 28.79 %, respectively. Moreover, introduction of reductive hydrazine hydrate stabilized the panchromatic   luminescent characteristics of the full-color CQDs, avoiding excessive oxidation and even unacceptable blue-shift in the resulting emission spectra in aqueous solutions. Moreover, the synthesized full-color CQDs were successfully applied to fabricate anti-counterfeiting textiles by coating technique, achieving high durability and encouraging information encryption effect. It is noteworthy that the presented work constitutes an alternative for synthesis of full-color fluorescent CQDs and expands it potential applications for preparation of various anti-counterfeiting fiber-based products.