Broadband and dynamic afterglow photoluminescent carbon dots for time-resolved optical information coding and encryption

Afterglow photoluminescent (PL) carbon dots (CDs)-based materials with tunable and time-dependent colors are highly desirable for their potential applications in high-level information encryption and anti-counterfeiting, but their construction remains a significant challenge. Herein, we report several broadband and dynamic afterglow PL CDs@BA using 2,2′-Dithiodibenzoic acid (DTSA) as the precursor of CDs and boric acid (BA) as the matrix. A facile thermal treatment significantly regulates the distribution among the cyan-green emission edge states and red emission surface states associated with the oxygen-containing groups of CDs@BA. The balanced contributions from different emissive states with distinct spectra, lifetimes on both nanoseconds and milliseconds scales, and relative proportions endow the CDs@BA with the ultrabroad and afterglow PL that cover almost the entire visible region. The broadband PL under light excitation mainly originates from the emissions of different singlet states, and the broadband afterglow PL is attributed to the combined delayed fluorescence (DF) of different singlet-triplet states. In particular, CDs@BA demonstrates an evident time-dependent afterglow color changing from tangerine to cyan-green, due to an enhanced contribution to the afterglow from the red DF component. Furthermore, these CDs@BA manifest promising potentials for white-light display, optical encryption, and time-resolved anti-counterfeiting applications. Our findings provide an effective strategy to construct broadband and dynamic afterglow CDs-based materials and are significant for understanding the related photophysical mechanisms.