Tetrachromatic CDs based on carbonation degree gradient: natural/synthetic precursor synergistic modulation and luminescence mechanism

Carbon dots (CDs), known for their notable fluorescence, cost-effectiveness, and eco-friendliness, hold substantial promise in versatile applications. However, existing one-pot strategies using biomass precursors predominantly yield blue-green emissive CDs, and achieving multicolor emission (especially red) remains challenging. In this work, four distinct fluorescent CDs (blue, green, yellow, and red) were synthesized via a one-pot solvothermal method using a synergistic natural/synthetic precursor system (Radix Saposhnikoviae and p-phenylenediamine). Systematic characterization revealed that the emission red shift (450 nm to 626 nm) is primarily governed by increased carbonization degree, as evidenced by the gradual enhancement of graphitic nitrogen content and sp² domain ordering. The synthetic precursor (p-phenylenediamine) drives carbon core growth and graphitization, while the natural biomass (Radix Saposhnikoviae) facilitates multi-scale carbonization control, enabling color diversification in a single pot. By integrating the four CDs with silicone resin on a 395 nm UV chip, we fabricated a warm white LED with high-quality white light with CIE chromatic coordinates (0.36, 0.35) and correlated color temperature 4428 K, demonstrating their practical potential in solid-state lighting.