Carbon dot composites of multicolor dual-mode phosphorescence and thermally enhanced delayed emission

Development of materials exhibiting both multicolor room-temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF), with tunable afterglow characteristics, is still a challenge. In this work, a surface engineering method is employed to obtain carbon dots (CDs) with dual multicolor RTP and TADF. These CDs achieve maximum quantum yield of 39.97 % and lifetime of 1.82 s, with visible luminescence persisting up to 15 s. Additionally, the CDs-IV composites demonstrate dual emissions, featuring yellow RTP and red TADF, with approximately 250 % increase in intensity at 640 nm, with long lifetime up to 115 ms as temperature rises from 313 to 358 K. This enhancement is achieved by integrating seed CDs into the ionic crystal matrix, which enhances reverse intersystem crossing by increasing spin-orbit coupling between singlet and triplet states while reducing non-radiative decay, resulting in a thermally enhanced TADF response. The robust interaction within the crystal network effectively stabilizes the triplet state, ensuring the material's stability in water and resistance to harsh conditions, such as strong acids and oxidants.