N-Dopant Site Formulation for White-Light-Emitting Carbon Dots with Tunable Chromaticity

Multicolor emissions from carbon dots (CDs) are vital for light-emitting diodes (LEDs), particularly for direct, white light emission (WLE), which enables a replacement of rare earth (RE)-doped phosphors. However, the difficulty of synthesizing single-component WLE CDs with full-spectrum emission severely hinders further investigation of their emission mechanisms and practical applications. Here, we demonstrate rational design and synthesis of chromatically tunable CDs with cyan-, orange-, and white-light emission, precisely tunable along the blackbody Planckian locus by controlling the ratio of different nitrogen dopant sites. We adopted 15N solid-state nuclear magnetic resonance (NMR) spectroscopy and X-ray photoelectron spectroscopy (XPS) to identify and quantify N-dopants in different sites and environments, and we explain their influence on emission properties of these CDs. This study provides guiding principles to achieve spectrally tuned emissions, enabling us to design WLE from CDs. This study also clarifies which chemical reagents and their proportions should be used for solvothermal synthesis to realize well-defined WLE from single-component CDs and adjustable, correlated color temperature (CCT) from 6500 to 3500 K. We also demonstrate a soft lighting device by adopting an optical haze film composed of cellulose fibers with excellent light-tailoring characteristics. The proposed methodology for synthesizing WLE CDs by engineering the N-doping sites will boost the development of lighting devices with readily available materials toward realization of low-cost, environmentally friendly WLEDs, solar cells, UV-blockers, counterfeit inks, and display applications.