Regulating red-shifted phosphorescence of carbon dots via introducing magnesium chloride

Achieving the multicolor phosphorescence of carbon dots (CDs), particularly with controllable wavelengths, remains a challenging yet desirable goal. Herein, we designed and prepared phosphorescent CDs (CDs@Al₂O₃ and CDs@MgAl₂O₄) using an in situ synthesis strategy. The oxygen vacancies in CDs stabilized the triplet excitons, thus enabling the long-lived and strong phosphorescence of these CDs. Importantly, CDs@MgAl₂O₄ exhibited obviously red-shifted phosphorescence (552 nm) compared to CDs@Al₂O₃ (525 nm) owing to increased conjugation and a narrowed bandgap, with the narrowed gap derived from coordination between magnesium and C[double bond, length as m-dash]O. These CDs showed excitation-dependent phosphorescence, which was tunable from cyan to red by varying excitation wavelengths. Additionally, we synthesized a series of phosphorescent CDs by employing different carbon sources, among which the magnesium-doped CDs consistently displayed red-shifted phosphorescence, thus proving the universality of this strategy and providing an innovative approach for regulating the phosphorescence of CDs.