Efficient tuning of nitrogen-doped carbon dots phosphorescence based on substrate regulation for multicolor and time-dependent anti-counterfeiting

The development of an accurate phosphorescent regulation strategy is key to customizing carbon dots (CDs) for anti-counterfeiting applications. To this target, we design a simple substrate regulation technique to manipulate phosphorescence of nitrogen-doped CDs (NCD). In this work, a cost-effective and environmentally friendly approach is proposed for combining NCD with urea (UA), boric acid (BA) and silica (SiO2) through hydrogen bonding or covalent bonding, a series of RTP composites were designed and synthesized. The RTP wavelength and lifetime of the composites can be tuned effectively, by preparing composite materials (NCD/UA, NCD/BA and NCD/SiO2) composed of NCD and different substrate (UA; BA; SiO2). The average RTP lifetime of NCD/UA, NCD/BA and NCD/SiO2 are 332.26 ms, 652.05 ms and 1587.22 ms, respectively. Furthermore, the RTP mechanism is verified. This facilitates the application of RTP materials and the adjustment of properties to practical requirements. Owing to the different phosphorescent wavelength and lifetime of NCD/UA, NCD/BA and NCD/SiO2, time-dependent multiple anti-counterfeiting can be achieved. Cell experiments show that NCD, NCD/BA, NCD/UA and NCD/SiO2 have low cytotoxicity and good biocompatibility. This result indicates these RTP materials can be potentially used to realize multicolor and time-dependent anti-counterfeiting.