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

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.