Ultra‐Narrow‐Bandwidth Deep‐Red Electroluminescence Based on Green Plant‐Derived Carbon Dots

Abstract Deep‐red light‐emitting diodes (DR‐LEDs, >660 nm) with high color‐purity and narrow‐bandwidth emission are promising for full‐color displays and solid‐state lighting applications. Currently, the DR‐LEDs are mainly based on conventional emitters such as organic materials and heavy‐metal based quantum dots (QDs) and perovskites. However, the organic materials always suffer from the complicated synthesis, inferior color purity with full‐width at half‐maximum (FWHM) more than 40 nm, and the QDs and perovskites still suffer from serious problems related to toxicity. Herein, this work reports the synthesis of efficient and high color‐purity deep‐red carbon dots (CDs) with a record narrow FWHM of 21 nm and a high quantum yield of more than 50% from readily available green plants. Moreover, an exciplex host is further established using a polymer and small molecular blend, which has been shown to be an efficient strategy for producing high color‐purity monochrome emission from deep‐red CDs via Förster energy transfer (FET). The deep‐red CD‐LEDs display high color‐purity with Commission Internationale de l'Eclairage (CIE) coordinates of (0.692, 0.307). To the best of the knowledge, this is the first report of high color‐purity CD‐LEDs in the deep‐red region, opening the door for the application of CDs in the development of high‐resolution light‐emitting display technologies.