Glass-crystallized far-red-emitting ceramics for high-power, spectrally matched plant-growth light sources
Lei Yang, Guojun Zheng, Chuan Liao, Jianrong Qiu, Wenge Xiao
Abstract
High-brightness far-red light plays a key role in increasing the photosynthetic efficiency and thus crop production in plant factory, as it regulates the entire lifecycle of plants, from seed germination to flowering and fruiting. However, the optical power and efficiency of far-red phosphor-converted light-emitting diodes, an inexpensive solid-state light source, are still limited due to the poor chemical stability and low thermal conductivity of conventional phosphor-silicone composite converters. Here, a series of Cr<sup>3+</sup> activated far-red-emitting silicate ceramics with near-unity internal quantum efficiency and near-zero thermal quenching are developed by a simple modified annealing method for full crystallization from the designed glass precursors. Furthermore, the local crystal field of octahedral Cr<sup>3+</sup> sites in Y<sub>2</sub>CaAl<sub>4</sub>SiO<sub>12</sub>:Cr<sup>3+</sup> is strengthened by cation substitution of Ba<sup>2+</sup> for Ca<sup>2+</sup> so that the emission spectrum is largely regulated from broad near-infrared band to narrow far-red band well overlapping with the absorption band of the phytochrome <em>P</em><sub>fr</sub> state. Finally, the optimized Y<sub>2</sub>Ca<sub>0.3</sub>Ba<sub>0.7</sub>Al<sub>4</sub>SiO<sub>12</sub>:Cr<sup>3+</sup> ceramic enables the realization of a high wall-plug efficiency of 27% for the far-red pc-LED and a record output optical power exceeding 2.1 W for the laser-driven far-red light source, highlighting its tremendous potential to serve as all-inorganic color converters for high-power plant-growth light sources.