Time-Dependent Room Temperature Phosphorescence Colors from Sulfur-Doped Carbon Dot-Based Composite for Advanced Information Encryption and Anti-Counterfeiting

The phenomenon of color time-dependent afterglow has a huge potential to improve the security levels in information encryption and anti-counterfeiting. Still, developing multiple triplet emission centers in long-lived afterglow materials is a formidable challenge. In this work, we developed carbon dots (CDs) based composite material (SCD@BA1) with time-dependent afterglow color from yellow to green within 2 s (excited by 360 nm irradiation) through sulfur introduction in CDs. SCDs are embedded in BA/B₂O₃ matrix materials via covalent bonds, and the sulfur dropping regulates the bandgap of the SCDs and new emission center with yellow RTP generated in 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. The two triplet emissions with different color and decay lifetimes lead to the phenomenon of afterglow color time-dependent. Simple concepts of time-limited information encryption and anti-counterfeiting were developed to demonstrate the great potential of SCD@BA1 composite in advanced security applications.