Nitrogen/Oxygen Co-Doped Carbon Quantum Dots with Efficient High Color-Purity Red Emission for Bright Electroluminescent LEDs.

Carbon quantum dots (CQDs) are emerging eco-friendly emitters for display and lighting technologies. However, achieving simultaneously high photoluminescence quantum yield (PLQY) and narrowband pure-red emissiona critical requirement for wide-gamut display applicationshas remained a significant challenge due to strong exciton-vibrational coupling. Here, we report high color-purity red emissive nitrogen/oxygen co-doped CQDs (HCP-RCQDs) featuring a rigid and planar π-conjugated structure. These HCP-RCQDs exhibit a high PLQY over 90%, a sharp emission peak at 645 nm with a full-width at half-maximum of 33 nm, and precise color coordinates of (0.71, 0.29)-closely matching the Rec. 2100 standard for red emitters. Experimental investigations and theoretical calculations reveal that the co-doped rigid π-conjugated system, feature well-bound potential energy surfaces that suppress exciton-vibration coupling and minimizes geometric reorganization, enabling both high efficiency and narrow emission. Moreover, by incorporating HCP-RCQDs in a thermally activated delayed fluorescence host and using phosphorescent sensitizers to facilitate energy transfer and maximize exciton utilization, we demonstrate bright and multicolor CQD-LEDs with a luminance of 18,535 cd m-2 and tunable color coordinates. This work presents a rational structural design strategy for CQDs with exceptional optical performance, opening new avenues for sustainable, high-definition optoelectronics.