Toward 95.5% Efficient Red Emissive Carbon Dots: Oxidation State Enhancing Radiative Electron-Transition of Indole Fluorophore

Red fluorescence carbon dots (CDs) are promising for diverse applications and have attracted tremendous research interest. However, it is still challenging to achieve red fluorescence CDs with high fluorescence quantum yields (QYs > 50%). Herein, three kinds of red fluorescence CDs with QYs of 53.48, 85.21, and 59.18% are prepared. Benefiting from the oxidation induced by atmospheric-pressure O₂ plasma processing, 95.5% efficient red fluorescence emission is achieved. It is revealed that the indole based fluorophores act as the red-emitting photoluminescence center. The synergistic effect between the C-O-C structure and indole based fluorophores plays a key role in promoting the efficiency of radiative electron transition and controlling the red fluorescence QYs. Additionally, the CDs show promising prospects for in vivo bioimaging and low in vivo toxicity. This work shows a new way for achieving high-efficiency red fluorescence CDs, and it may guide the development of high-performance CDs for diverse applications.