Excitation-wavelength-dependent switchable afterglow from carbon-dot-embedded composites for dual-mode information encryption.

Carbon dot (CD)-based afterglow composites have attracted significant interest for anti-counterfeiting, encryption, and bioimaging applications owing to their excellent optical properties, controllable cost, low toxicity, and environmental friendliness. However, conventional CD-based afterglow materials generally suffer from limitations including unsatisfactory structural stability, inefficient exciton utilization, and limited anti-counterfeiting potential. Therefore, there is an urgent need to develop diverse rigid matrix materials and precisely control the interactions between the matrix and CDs to achieve controlled preparation of CD-based dual-mode afterglow materials. Phenylboronic acid (PBA), with its hydroxyl and boronic acid groups, could effectively modulates CD surface states and stabilizes triplet excitons to a great extent, which is expected to serve as a promising matrix for high-performance CD-based afterglow materials. Herein, we employed a matrix-assisted strategy by embedding Cu, N-CDs with dual emission centers into a PBA matrix to construct a composite material (Cu, N-CDs@PBA) exhibiting tunable afterglow and time-evolving afterglow phenomenon during the preferred heat treatment process. The structural evolution of PBA during this heat treatment and its influence on afterglow properties were systematically investigated. The composite exhibits unique luminescence characteristics under different excitation wavelengths: blue room temperature phosphorescence (RTP) under 265 nm excitation, green RTP under 365 nm excitation, and delayed fluorescence under 450 nm excitation. These distinct emissions originate from the energy-level matching and coupling interaction between the matrix and the different emission centers of the Cu, N-CDs. Leveraging its tunable afterglow, Cu, N-CDs@PBA composite was applied as a cost-competitive and sustainable anti-counterfeiting tag for information encryption, demonstrating fascinating development prospects.