Recent progress of inorganic phosphors in artificial plant cultivation LEDs

Abstract

Phosphor-converted light emitting diodes (pc-LEDs) have become a promising and ideal supplemental illumination source for modern environment-controlled agriculture owing to their efficiency, energy saving potential, small size, low cost, long lifetime and, especially, tunable output spectra. The light absorption of photoreceptors, such as chlorophyll-a/b and carotenoids, in plant photosynthesis dominantly falls in the blue (350–480 nm) and red (600–680 nm) regions. The far red (680–730 nm) light are absorbed by phytochromes to adjust flowering, while the near-infrared (NIR, 800–1100 nm) light are absorbed by photosynthetic bacteria to assist biological nitrogen fixation of plant roots. To better match the absorption spectra of plant growth pigments for enhancing the yield and quality of crops, a spectral matched pc-LED for plant growth was achieved by adjusting the phosphor. Recent research progress on corresponding mono- or multi-color emission phosphors suitable for plant growth pc-LED lamps was reviewed, including blue, red/far-red, near-infrared, and white or full-color phosphors, which can balance between plant requirements and human eye comfort. Besides, the strategies for spectral design and improvement of the luminescent properties of phosphors are summarized. Notably, phosphors, which do not affect plant rhythms, are also briefly introduced, and the safety of phosphors in vivo for promoting plant growth is emphasized. Finally, an outlook is provided based on the current challenges for plant growth pc-LEDs.