Customized NIR‐II Dual‐Phase Carbon Dots: Elucidating the Emission Mechanism for Smart Photonic Applications

ABSTRACT Carbon dots (CDs) exhibiting dual‐phase photoluminescence (PL) in the second near‐infrared window (NIR‐II, 900–1700 nm) region have shown considerable potential for applications in information encryption, lighting, and bioimaging. However, significant challenges remain owing to a lack of reliable design strategies. In this study, high‐brightness dual‐phase NIR‐II PL CDs (NIR‐CDs) were successfully prepared for the first time employing innovative strategies. NIR‐CDs possess a distinctive core–shell structure, and the donor–acceptor interactions between the carbon core and strong electron‐donating groups on the shell effectively induce a charge‐transfer state. The NIR‐CDs exhibited a fluorescence quantum yield (QY) of up to 5.91% at 920 nm in conjunction with excellent stability. Notably, the rich functional groups on the shell of NIR‐CDs provided hydrogen bonding sites, enabling a 960 nm fluorescence emission and high absolute QY of 3.82% in the solid state. The dual‐phase PL of NIR‐CDs enables their use in NIR‐II multilevel information encryption and fingerprint authentication. The NIR‐II flexible film based on NIR‐CDs exhibits excellent fluorescence stability under various external stimuli. Furthermore, the quick response code based on NIR‐CDs remains clearly identifiable beneath 3 mm porcine tissue, which highlights their potential for anti‐counterfeiting, encryption, and bioimaging sensing.