Dual‐Emission Self‐Protective Phosphorescent Carbon Dots with Ultra‐Long Lifetime and Time‐Dependent Afterglow Colors for Tri‐Mode Encryption

Abstract Developing matrix‐free phosphorescent carbon dots (CDs) with tunable color emission and exceptionally long lifetimes is highly desirable for sophisticated information encryption. However, the majority of reported matrix‐free CDs demonstrate only single‐color emission and short lifetimes, restricting their practical applications. Herein, dual‐emission self‐protective room temperature phosphorescent CDs (DE‐CDs) with ultra‐long lifetimes and time‐dependent afterglow colors are prepared. These DE‐CDs are synthesized through a microwave heating process involving 1‐butylamine and phosphoric acid aqueous solution. By adjusting excitation wavelength, they display green and yellow phosphorescence with ultra‐long lifetimes of up to 1.25 and 1.74 s, respectively, representing the longest lifetime among matrix‐free green and yellow CDs to date. The dual emission is attributed to the coexistence of a high‐energy state within the carbon core and a low‐energy state associated with C─N/C═N bonds on DE‐CDs surface. The ultra‐long lifetimes originate from the self‐protective internal hydrogen bonds formed between P and N heteroatom‐containing functional groups on the dot surface, which stabilize the emissive species. Intriguingly, under 365 nm irradiation, the afterglow color transitions from yellow to green due to differing triplet‐state decay rates. Leveraging these time‐dependent afterglow colors, a triple‐code mode is achieved for advanced dynamic encryption.