N, B-Codoping Induces High-Efficiency Solid-State Fluorescence and Dual Emission of Yellow/Orange Carbon Dots

Carbon dots (CDs) have attracted a lot of attention because of their tunable emission wavelength, high photobleaching resistance, and environmental friendliness. However, they suffer from aggregation-induced quenching in the solid state, which limits their application in solid-state fields. In this work, yellow- and orange-emissive N, B-codoped CDs (y-NB-CDs and o-NB-CDs) with highly efficient solid-state fluorescence and dual emission were achieved by a facile one-step microwave method. The obtained y-NB-CDs in the powder state show bright yellow fluorescence with a high solid-state QY of 39.0% and typical dual emission peaks at 484 and 565 nm. The as-synthesized o-NB-CDs in the powder state exhibit bright orange fluorescence with a high solid-state QY of 31.1% and dual emission at 484 and 585 nm. After systematically studying the effect of N, B-codoping on the solid-state fluorescence of NB-CDs, we demonstrate that the hydrogen bond between B–OH on the surface of the NB-CDs can inhibit the direct contact of nanoparticles, and a high content of graphitic N in NB-CDs can increase the probability of the radiative process of the aromatic domains, both of which trigger high-efficiency solid-state fluorescence of NB-CDs. This finding provides a general and efficient method for highly emissive solid-state CDs. In addition, N, B-codoping can also give NB-CDs dual emission in the short-wavelength and long-wavelength regions, ascribed to the carbon core and surface defect state, respectively. Finally, y-NB-CDs were demonstrated as a phosphor to prepare a near white light-emitting diode with a color rendering index of 84 by combining them with an ultraviolet chip.