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

Abstract 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.