Excitation-dependent room temperature phosphorescence carbon dots with ultralong lifetime for information encryption and delay illumination

Long-lifetime room temperature phosphorescent (RTP) carbon dots (CDs) have received extensive attention due to their potential applications in fields such as information encryption, sensing, and biological imaging. However, the rapid synthesis of RTP carbon dots with excitation wavelength dependence remains a challenge. Herein, Zn-CDs@B₂O₃ with excitation wavelength dependence were prepared by calcining a mixture of biuret, boric acid and zinc sulfate at 250 ℃ for 30 min. CDs are embedded into the rigid matrix (B₂O₃) through covalent bonds (B-C), which suppresses the non-radiative transitions and molecular vibrations of the CDs. The incorporation of N, O, B, and Zn atoms enhances intersystem crossing (ISC) and increases the spin–orbit coupling (SOC), the phosphorescence lifetime of Zn-CDs@B₂O₃ reaches up to 1.23 s. The Zn-CDs@B₂O₃ composite is notable for its vivid blue RTP under 254 nm excitation, visible for about 13 s, and it shifts to a bright green RTP excitated at 365 nm, lasting 8 s to the naked eye. The experimental results indicate that the excitation wavelength dependence of Zn-CDs@B₂O₃ may be attributed to the presence of multiple luminescent centers. Based on the aforementioned characteristics, the Zn-CDs@B₂O₃ were successfully used in the advanced information encryption and light emitting diodes (LEDs), the Zn-CDs@B₂O₃ show considerable promise for applications in information encryption and delay illumination.