Carbon Dots-Doped PVA Nanocomposite Films with Green-to-Red Light Conversion Properties Enhance the Productivity and Fruit Quality in Tomato

The inefficient utilization of green light by crop canopies have jointly limited the effectiveness of spectral regulation strategies in agriculture. Here, red-emitting carbon dots (CDs) were embedded in a poly(vinyl alcohol) (PVA) matrix to create sprayable nanocomposite films (PCDs) with CD concentrations of 0, 0.1, 0.25, and 0.5 mg/mL. Foliar application at tomato flowering converted green light to red light, increasing relative red contribution by 20% without photodamage. Treated plants showed enhanced chlorophyll content, photosynthetic rate, electron transport, and Rubisco activity, resulting in 41.2–43.4% higher shoot biomass and 49.5–58.3% higher fruit yield. Sensory evaluation of ripe fruits scored significantly higher in redness, sweetness, and overall flavor acceptability, with elevated lycopene, soluble sugar content, and sugar–acid ratio. These findings demonstrate that CDs-doped PVA nanocomposite films offer a practical, low-energy spectral conversion strategy to optimize light use efficiency, boost productivity, and improve fruit sensory quality in tomato.