Glass-crystallized far-red-emitting ceramics for high-power, spectrally matched plant-growth light sources

High-brightness far-red light plays a key role in increasing photosynthetic efficiency and thus crop production in plant factories, 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, which are inexpensive solid-state light sources, are still limited due to the poor chemical stability and low thermal conductivity of conventional phosphor‒silicone composite converters. Here, a series of Cr³⁺-activated far-red-emitting silicate ceramics with near-unity internal quantum efficiency and near-zero thermal quenching were developed via a simple modified annealing method for full crystallization from the designed glass precursors. Furthermore, the local crystal field of octahedral Cr³⁺ sites in Y₂CaAl₄SiO₁₂:Cr³⁺ is strengthened by cation substitution of Ba²⁺ for Ca²⁺ so that the emission spectrum is largely regulated from a broad near-infrared band to a narrow far-red band that overlaps well with the absorption band of the phytochrome (P_fr) state. Finally, the optimized Y₂Ca_0.3Ba_0.7Al₄SiO₁₂:Cr³⁺ 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.