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 C=P 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 S-1 to T-1 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.