Rapid one-step synthesis of self-quenching-resistant cellulose-derived solid-state emissive carbon dots for white LEDs

Cellulose-derived carbon dots (C-CDs), namely C₅-CDs and C₁₀-CDs, were synthesized via an ultrafast (5 or 10 min) one-pot hydrothermal reaction, exhibiting anti-aggregation-caused quenching and highly efficient solid-state fluorescence. Detailed studies on the structural composition and optical properties of the C-CDs showed that the presence of cellulose nanofibrils effectively inhibits π-π interactions between the carbon cores. The sp² hybridized carbon cores within the graphitic structure result in blue fluorescence. After further carbonization, fluorescence resonance energy transfer occurs between the graphitized carbon cores (donors) and molecular fluorophores (acceptors). The enhanced n-π∗ electronic transitions lead to surface state-dominated yellow-green emission. Simulations using density functional theory confirmed that increased amounts of graphitic N and CO bonds reduce the energy bandgap and thus promote longer wavelength emission. White light-emitting diodes (WLED), with near ideal white light (CIE 1931 coordinates (0.33, 0.33) and color rendering index >80) were produced using the blue- (C₅-CDs) and yellow-green-emitting (C₁₀-CDs) C-CDs as the color-conversion layer. The light, therefore, shows the true colors of illuminated objects. This strategy, which achieves ultra-short reaction times (≤10 min) and high solid-state quantum yields (40 %), establishes a viable pathway for the cost-effective production of biomass-derived carbon dots.