Phonon-Assisted Anti-Stokes Red Emission in Carbon Dots with Nitrogen-Containing Polyaromatic Domains

The outstanding and versatile luminescence of carbon dots has attracted extensive research interest, with significant progress achieved. However, current advances are based predominantly on their well-established Stokes emission, whereas their anti-Stokes photoluminescence remains largely underexplored. Herein, strong anti-Stokes photoluminescence is realized for carbon dots with nitrogen-containing polyaromatic domains (Anti-CDs) when excited by low-power continuous-wave light sources, with a maximal anti-Stokes shift up to ∼70 nm (∼0.19 eV energy gain). It is demonstrated that a phonon-assisted single-photon excitation process underlies this photon energy upconversion. Structural and theoretical analyses indicate that the N-containing polyaromatic domains in Anti-CDs are responsible for the formation of vibronic fine structures and provide channels for thermal population of higher ground-state vibrational levels, which is essential for anti-Stokes photoluminescence. Benefiting from their intense, long-wavelength anti-Stokes photoluminescence in aqueous environments, Anti-CDs are successfully applied to in vivo anti-Stokes photoluminescence imaging and information encryption.