Highly luminescent nitrogen and sulfur co-doped carbon dots for Sn 2+ and S 2- sensing and dual-mode anti-counterfeiting.

The preparation of nitrogen and sulfur co-doped carbon dots (N, S-CDs) with highly bright orange-red fluorescence is reported through a facile solvothermal approach with naphthalenetetracarboxylic dianhydride as starting material. The N, S-CDs exhibited superior properties, including intense long-wavelength emission with a narrow full width at half maxima (FWHM) of 33 nm, high fluorescence quantum yield (QY) of 60.5% in aqueous solution, excitation-independent emission behavior, and excellent water dispersibility. In addition, sulfide ions (S 2- ) could selectively recover the fluorescence of N, S-CDs quenched by Sn 2+ . The selective experiment suggested that the N, S-CDs/Sn 2+ complex could be used as a fluorescence-enhancement sensor for sulfide ions (S 2- ), with the linear range of 5-50 μM and the LOD of 0.35 μM. The practicality and feasibility of this sensor for the determination of sulfide ions in tap and lake water were verified with good recoveries. Furthermore, because of their highly bright fluorescence and strong water solubility, the N, S-CDs could be easily fabricated into fluorescent ink and transparent films, demonstrating the promising application in anti-counterfeiting. Therefore, the designed N, S-CDs exhibited the advantages of facile preparation, intense fluorescence, high stability, easy processing, and selective fluorescence change for specific analytes, which showed high potential in fluorescence detection and anti-counterfeiting.