The UV-blocking molecules convert UV light into thermal energy. The plastic covering films used in greenhouses contain UV-blocking materials. Thus, shading the plants from solar UV light is one of the key strategies to suppress photoinhibition and photodamages of the plants. UV-B (295–320 nm) is known to induce damage of DNA 15. In particular, UV-A (320–400 nm) light affects not only photo-inhibition of photosystem(PS)-II 15 but also increase of photosynthetic rate 16. Various plants respond to UV light 12, 13, 14. Sunlight is a sustainable energy source, however, it includes ultraviolet (UV) light, which is located in the high-energy wavelength region (200–400 nm). The photosynthetic action spectra have revealed that red light for excitation in the Qy band provides the highest photosynthetic quantum yield 11. The light color also affects plant growth, productivity, morphology, and physiology 8, 9, 10. The effective wavelengths for photosynthesis agree well with the absorption bands. In particular, land plants contain the chlorophyll- a and b pigments in light-harvesting antenna and reaction center apparatuses, which absorb visible light in the red (Qy band: 600–700 nm) and blue (Soret band: 400–450 nm) regions. In the initial stage of photosynthesis, chlorophyll pigments absorb sunlight and utilize solar photon energy for the production of bio-resources 7. Light energy is required by natural photosynthetic organisms such as higher plants, algae, and photosynthetic bacteria. Stimulating photosynthesis is a promising strategy to accelerate plant growth and biomass production 5, 6. Sustainable scientific and technological developments for future plant production are among the most important challenges associated with supplying sufficient global food and bioenergy in terms of world population growth, which is expected to reach nearly nine billion people by 2050 1, 2, 3, 4.
The present film can promote the plant production in fields of agriculture and forestry. The plants cultured with Eu 3+-painted films had a 1.2-fold height and 1.4-fold total body biomass than those cultures without the Eu 3+ luminophores. Eu 3+-painted films provide significant growth acceleration with size increment and biomass production for vegetal crops and trees in a northern region.
The present Eu 3+-based films absorb UV light and exhibit strong red luminescence under sunlight. In this study, transparent films equipped with a UV-to-red wavelength-converting luminophore, the Eu 3+ complex, were prepared on commercially available plastic films for plant growth experiments. Ultraviolet (UV)-to-red wavelength-converting materials are promising candidates for eco-friendly plant cultures that do not require electric power. Red light is useful for plant growth because it is absorbed by chlorophyll pigments, which initiate natural photosynthetic processes. The stimulation of photosynthesis is a strategy for achieving sustainable plant production.
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