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

Abstract 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 Eu 3+ ‐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 Eu 3+ ‐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.