Photo-induced Ag modulating carbon dots: Greatly improved fluorescent properties and derived sensing application

Carbon dots (CDs) have been attracted much attention and widely studied due to their excellent fluorescence (FL) properties, better biocompatibility and outstanding photo/chemical stability. However, the disadvantage of lower quantum yield (QY) still limits its wide application. Herein, we reported a novel and convenient strategy to prepare photo-induced Ag/CDs (p-Ag/CDs) by irradiating the mixed Ag+ and hydrophobic CDs (h-CDs) acetone solution with ultraviolet (UV) light. The obtained p-Ag/CDs exhibit a greatly enhanced FL emission together with a blue shift (460 nm) than h-CDs (520 nm). The QY of p-Ag/CDs is measured to be 51.1%, which is 10.4 times higher than that of h-CDs (4.9%), indicating that photo-induced Ag modulation can effectively improve the optical properties of CDs. The mechanisms for the FL enhancement and blue shift of h-CDs are studied in detail. The results prove that the greatly enhanced FL emission is from the generated Ag nanoparticles (AgNPs) by UV light irradiation based on metal-enhanced fluorescence (MEF), and the increased oxygen-contained groups in this process lead to the blue shift in CDs fluorescence. Interestingly, the p-Ag/CDs exhibit higher sensitivity and selectivity for sulfide ions (S2−) detection than that of h-CDs, which have a lower response to S2−. This work not only offers a novel strategy to improve the FL properties of materials but also endows them with new functions and broadens their application fields.