Adjusting TADF and Phosphorescence for Tailored Dynamic Time-Dependent Afterglow Colored Carbon Dots spanning Full Visible Region

Abstract

Time-dependent afterglow colored (TDAC) behavior differs from static afterglow by involving wavelength changes, enabling low-cost, high-level encryption and anti-counterfeiting. However, the existing carbon dot (CD)-based TDAC materials lack a clear mechanistic explanation and controllable wavelength changes, significantly hindering the progress of practical applications in this field. In this study, we synthesized CDs composites with customizable tunable TDAC wavelengths across the visible region. Furthermore, we elucidated the underlying mechanism of TDAC that exhibits sequential weakening and relative strengthening of long- and short-wavelength afterglow centers. This phenomenon arises due to strong emission with a short lifetime originating from long-wavelength thermally activated delayed fluorescence (TADF), along with weak emission having a longer lifetime originating from short-wavelength phosphorescence. The presence of surface-rich carboxyl groups on CDs determines the short-wavelength afterglow in their dispersed state while their high conjugation degree governs the long-wavelength afterglow in their aggregated state. Additionally, appropriate doping levels of CDs enhance color change phenomena during afterglow. Finally, by embedding CDs into different rigid matrix, the range of afterglow changes can be tailored arbitrarily within the visible light region. Leveraging these exceptional TDAC characteristics has allowed us to successfully develop advanced 4D coding technologies that facilitate multi-mode anti-counterfeiting and dynamic information encryption.