Synthesis of Phosphorescent Carbon Dot Composite with Redshift Emission by Annealing Treatment for Bioimaging

Room-temperature phosphorescent carbon dots (RTP CDs) are promising afterglow materials applied in bioimaging owing to their long-lived emission and biocompatibility. Achieving RTP CDs with long emission wavelengths in aqueous environments remains challenging because of the influence of surface and carbon core states of CDs on luminescence. Herein, thermally annealed solid CDs encapsulated with SiO₂ are developed in this work to obtain yellow-green RTP CD composites (A-CDs@SiO₂) with redshifted emission wavelengths. After thermal annealing, the carbonization degree of CDs increases, resulting in a redshift of their optimal phosphorescence emission wavelength from 500 to 525 nm, and the phosphorescence lifetime of CDs reaches 926.97 ms. Additionally, the optimal phosphorescence emission wavelength of A-CDs@SiO₂ is 513 nm. SiO₂ encapsulation restricted the movement of luminescent centers, thereby extending the phosphorescence lifetime of CDs in aqueous solution to 1263.40 ms. Biological imaging experiments confirmed that the obtained A-CDs@SiO₂ exhibited significant phosphorescence signals in mice with a phosphorescence intensity of 1.490 × 10⁵ p/(s cm² sr), and the phosphorescence signals can still be collected after re-excitation within 1 h. Therefore, as a bioluminescent afterglow probe, A-CDs@SiO₂ demonstrates great potential in bioimaging.