A Bright and Stable Violet Carbon Dot Light-Emitting Diode

Violet light-emitting diodes (LEDs) with emission at 400 nm are very important for solid-state lighting, high-density information storage, display technology, and biology medical treatment. Wide band-gap semiconductors and/or the semiconductor quantum dots (QDs), typically based on heavy metals such as cadmium and lead, are promising candidates for the violet LEDs, but so far these have had external quantum efficiencies (EQEs) lower than 0.31% (luminance 147.6 cd cm(-2); 410 nm). Herein, violet light-emitting materials and the violet LED devices based on carbon dots (CDots) are presented. The CDots have absolute photoluminescence quantum yield of 23.9% and produce two-narrow-peak emission at 382 and 401 nm with narrow full-width at half-maximum about 30 nm, respectively. The violet LEDs based on these CDots display high performance with a maximum luminance of 163 cd m(-2) (electroluminescence peak located at 408 nm; Commission International de I'Eclairage color coordinate (0.180, 0.121)) and high EQE of 0.831%, exceeding that of previously reported semiconductor QDs-based violet LEDs. Moreover, these CDots-based violet LEDs have a high current efficiency of 0.62 cd A(-1), a long lifetime (T-50, 50 h), as well as a low turn-on voltage of 3.7 V.