Plant Habitat-Conscious White Light Emission of Dy³⁺ in Whitlockite-like Phosphates: Reduced Photosynthesis and Inhibition of Bloom Impediment

It has been pointed out that agricultural crops and other natural plants may be damaged by outdoor lighting systems. Therefore, lighting that does not affect plant growth is needed. To address this problem, we have prepared a new whitlockite-like phosphate Dy-phosphor Ca8MgY1-x-yLaxDyy(PO4)7, which exhibits a yellow-white Dy(3+) luminescence that has a maximum internal quantum efficiency of 65.6% under a 387 nm excitation light for x = 0.10 and y = 0.05. The x dependence of IQE showed two maxima at x = 0.10-0.15 and 0.80-0.85, which could be due to the partial allowance of f-f forbidden transitions by local lattice distortion around the Dy(3+) ions originating from the La incorporation at near end members of Ca8MgY1-x-yLaxDyy(PO4)7. Concentration quenching occurred for x > 0.05. A white light-emitting diode (LED) was fabricated from a UV LED emitting at 385 nm and a Ca8MgY1-x-yLaxDyy(PO4)7 phosphor (Dy-WLED) for which the CIE color coordinates and correlated color temperature were CIE(0.350,0.378) and 4919 K, respectively. Plant cultivation experiments on Chlorella photosynthetic growth and blooming of the short-day plant Cosmos were carried out using the prepared Dy-WLED and reference commercial LEDs. We found that the Dy-WLED substantially reduced the photosynthesis of Chlorella and inhibited bloom impediment in Cosmos. These effects originated especially from the reduction of red-near-IR emissions. Thus, we conclude that the Dy-WLED is a very promising candidate for plant habitat-conscious white LEDs for outdoor lights that can protect both natural plant habitats and crop yields.