Carbon dots with efficient solid-state red-light emission through the step-by-step surface modification towards light-emitting diodes

Carbon dots (CDs) have attracted extensive attention over the past decade due to their excellent advantages. However, few attempts have been reported for realizing the long-wavelength emission, especially for obtaining efficient solid-state red emission with high photoluminescence quantum yield (QY). Herein, we developed highly red light emitting CDs by the step-by-step surface modifications of the nitrogen-doped CDs. By introducing hexadecyltrimethyl ammonium bromide to modulate a red CD aqueous solution, the photoluminescence QY increases from 23.2% to 43.6%. Furthermore, we dispersed CDs in a PVP matrix for a solid-state film, where the solid-state quenching was effectively suppressed, and high QY (41.3%) of red light emission was achieved. Taking advantage of the as-prepared red light emitting CDs combining with the reported high quantum yield blue and green light emitting CDs, we realized UV-pumped WLEDs with tunable correlated color temperature from 7879 to 2961 K. Moreover, a high color rendering index (CRI) of 93 for WLEDs was realized, which is superior than the best records for the semiconductor quantum dot based WLEDs. Finally, the red light emitting CDs were demonstrated to have promising application as a red color converter in traditional YAG-based WLEDs to improve their CCT and CRI.