The synthesis and application of an excitation-dependent ultra-long lifetime room temperature phosphorescence carbon dot composite

Recently, room temperature phosphorescence (RTP) materials have gained widespread attention owing to their superior photophysical properties. However, it is still a challenge to realize color-tunable RTP with ultra-long lifetime in the same material through a simple strategy. Herein, we report an excitation-dependent ultra-long lifetime RTP carbon dots (CDs) composite though embedding N,O-doped CDs into an insoluble phosphate (IP) matrix (named N,O-CDs@IP). The formation of CP covalent bonds suppresses the non-radiative transition of triplet excitons and therefore activates chromogenic functional group CO. The N,O-CDs@IP composite exhibits excitation-dependent phosphorescence. When the excitation wavelength increases from 254 to 365 nm, the phosphorescence emission varies from cyan (482 nm) to green (518 nm) with ultra-long lifetimes of 2.04 s and 1.15 s, respectively. The phosphorescence quantum efficiencies at 482 and 518 nm are 24.7% and 19.88%, respectively. The excitation-dependent phosphorescence would be caused by the excitation transfer paths being different from S1 to T1 such that the energy levels are different under different excitation wavelengths in the aggregated state. Our synthesized N,O-CDs@IP can be used in fingerprint identification and anti-counterfeiting. This indicates that the N,O-CDs@IP composite has great potential in intelligent coding and advanced information encryption.