Transparent, Sprayable Plastic Films for Luminescent Down-Shifted-Assisted Plant Growth

The world's steadily growing population and global heating due to climate change are a threat to food security. To meet this challenge, novel technologies are needed to increase crop production in a sustainable way. In this work, the use of luminescent down-shifting (LDS) materials based on molecular Eu³⁺-containing polyoxotitanates for plant growth enhancement is investigated. Using a systematic design strategy to optimize down-shifting properties, conversion of the ultraviolet spectral range to the photosynthetically active radiation (PAR) is achieved with quantum yields as high as 68%. The prototype Eu³⁺-compound can be incorporated into water-based acrylic varnish that can be spray-coated onto existing greenhouses. Comparing coated with uncoated greenhouses, basil plants produce 9% more leaf dry weight per plant, and a highly significant 10% increase in individual leaf dry weight. The coating reduces the amount of transmitted PAR by 8% but has advantageous effects on diffuse radiation and in reducing the internal mean temperature. Although there is some uncertainty as to the contribution of down-shifting, with the bulk of the increase probably being due to higher diffused light and the reduction in maximum daily temperatures, this study establishes a model for the design of LDS paints for real-world agricultural applications.