Time-dependent room temperature phosphorescent colors from a sulfur-doped carbon dot-based composite for advanced information encryption and anti-counterfeiting applications

The phenomenon of a time-dependent afterglow color change has huge potential to improve the security levels in information encryption and anti-counterfeiting. However, developing multiple triplet emission centers in long-lived afterglow materials is a formidable challenge. In this work, we developed a carbon dot (CDs) based composite material (SCD@BA1) with a time-dependent afterglow color change from yellow to green within 2 s (excited by 360 nm irradiation) by introducing sulfur into CDs. SCDs are embedded in BA/B2O3 matrix materials via covalent bonds, and the sulfur doping regulates the bandgap of the SCDs, and a new emission center with yellow room temperature phosphorescence (RTP) is generated on the CD surface. The rigid structure of the composite promotes the high-energy green RTP emission in the carbon core state and low-energy yellow RTP emission in the surface state simultaneously, activated under irradiation of approximately 360 nm light. The two triplet emissions with different colors and decay lifetimes lead to a phenomenon of a time-dependent afterglow color change. Simple concepts of advanced time-limited information encryption and anti-counterfeiting were developed to demonstrate the great potential of the SCD@BA1 composite for advanced security applications. Sulfur doping regulates the bandgap of the carbon dots, and time-dependent afterglow color emission is realized in a carbon dot-based composite via the multiple triplet emissions with distinct lifetimes.