Designing core–shell structured carbon nanodots to guide ultraviolet-to-red conversion for preparation of healthy plant-growth LEDs

Red light plays a crucial role in plant growth. However, the lack of functional materials suitable for red light emission under ultraviolet excitation limits the ability of ultraviolet light sources for greenhouse illumination. Solid-state carbon dots, serving as alternatives to rare-earth phosphors, typically achieve red emission by narrowing their bandgap through defect introduction, an increased particle size, and enhanced conjugation. However, bandgap reduction often induces a red-shift of the excitation wavelength. Therefore, the excitation spectrum of solid-state red-emitting carbon dots is currently mainly concentrated in the long-wavelength visible light region, which cannot meet the needs of ultraviolet light-emitting LEDs in the field of greenhouse illumination. To address this, we designed core-shell structured solid-state carbon nanodots, leveraging synergistic effects between the core and shell layers to achieve highly efficient red light emission. When excited with ultraviolet light (362 nm), the carbon nanodots emit red fluorescence (619 nm), with a Stokes shift as large as 257 nm. Furthermore, a light conversion film was fabricated by compositing the carbon nanodots with PMMA and then integrated with a UV-LED as a light source for indoor plant cultivation, effectively promoting healthy plant growth. In summary, the solid-state red-emitting carbon nanodots synthesized in this study exhibit broad application prospects in both ultraviolet light utilization and plant illumination fields.