Spirulina-derived carbon dots with narrow-peak NIR emission for LED applications

Biomass carbon dots are gaining attention because of their natural characterizations of sustainability and eco-friendliness. However, most biomass carbon dots only emit blue fluorescence, and their quantum yields are usually poor. Most biomass carbon sites have a complex biomass composition, rendering it hard to effectively analyze their fluorescence emission mechanisms. This is especially true for near-infrared emission carbon dots derived from biomass. In this paper, nitrogen-rich biomass spirulina was used as a carbon source and modified with the nitrogen-containing reagent ethanolamine as a nitrogen dopant. Blue-light carbon dots (B-CDs) and red-light carbon dots (R-CDs) were successfully prepared by microwave method. B-CDs and R-CDs have narrower half-width peaks (FWHM), with R-CDs having an FWHM of only 27 nm. In-depth experimental analyses showed that the synergistic effect of the large sp² conjugation domains and the amide groups could modulate energy gap of CDs and red-shift the emission peak of CDs to 660 nm, which realized the fluorescence tunability of the biomass-based CDs. In addition, the higher nitrogen doping ratio increased the fluorescence quantum yield of the carbon dots from 22.76 % for B-CDs to 45.68 % for R-CDs. B-CDs/R-CDs exhibited bright white/red luminescence in the solid state under UV excitation. Finally, fluorescent films, white LEDs (WLEDs), and red LEDs (RLEDs) were prepared using white and red carbon dots as phosphors. The work in this paper greatly contributed to the resourceful utilization of the bio-pollutant spirulina and also highlighted potential value of spirulina-based carbon dots in LEDs.