Highly Efficient Wavelength Red‐Shift Regulating Strategy of Carbon Dots Composites via the Effective Conjugated Domain and the Hydrogen Bonding Synergy

Abstract Room‐temperature phosphorescent (RTP) materials hold significant potential for applications in lighting, anti‐counterfeiting, and multi‐level information encryption. However, regulating RTP emission wavelengths, especially shifting into the red spectral region, remains challenging due to the spin‐forbidden transitions of triplet‐state excitons and non‐radiative decay. To address this issue, carbon dots (CDs) with different conjugated domain sizes and phosphorescent potential are designed and synthesized. The CDs are then encapsulated in polyacrylamide (PAM), resulting in multicolored RTP emission ranging from cyan to red (465–635 nm), with cyan and red phosphorescence exceeding 10 s and 2 s, respectively. The mechanism suggests that the enhanced conjugation effect leads to energy level splitting and strengthened electron coupling, which lowers the energy gap between singlet and triplet excitons, ultimately causing a redshift in the phosphorescent emission wavelength. Meanwhile, the introduction of hydrogen bonding protects the excited state of the electrons, suppresses non‐radiative transitions, and induces RTP in the CDs. These materials are applied in multi‐level information encryption and time‐delayed LED illumination, offering novel strategies for high‐security technologies and advanced optical devices.