Tunable cold/warm white light emitting devices based on carbon dots with multiple emissive centers

Abstract

The correlated color temperature (CCT) of lighting is closely related to human emotions. However, there is still a relative lack of white light emitting devices (W-LEDs) with tunable CCT to meet application demands in different scenarios. Here, we develop a W-LED with tunable CCT based on multiple emissive centers of carbon dots (CDots) synthesized through controlled thermal carbonization of citric acid and urea. The reaction at 160 °C for 4 h results in amorphous CDots, which exhibit excitation wavelength dependent photoluminescence (PL) containing two peaks at 446 and 520 nm. However, by increasing the reaction temperature and duration, crystalline CDots are obtained, which show broad PL peaking at 650 nm. Based on their complementary spectral ranges, a W-LED with an extremely high color rendering index of 96 is demonstrated. Moreover, a W-LED with both 365 and 405 nm electroluminescent chips is designed. The W-LED shifts from cold to warm white, when the excitation chips switch from 365 to 405 nm. This adjustable CCT can create a harmonious, enjoyable, and safe lighting environment to meet the demands of different scenes.