Distorted double perovskite La2(Al0.5MgTa0.5)O6:Mn4+ deep-red emitting material: Crystal structure, luminescent properties, and applications in plant lighting.

Double perovskite oxides have emerged as pivotal host matrices for Mn4+-activated deep-red phosphors in recent years owing to their exceptional chemical stability and versatile structural tunability. In this study, a series of Mn4+-doped double perovskite La2(Al0.5MgTa0.5)O6 (LAMT) deep-red phosphors were synthesized via the high-temperature solid-state method. Their crystal structure, luminescent properties, and potential applications in plant lighting were systematically investigated. Within the LAMT structure, the [MgO6] and [Al/TaO6] octahedra undergo distortion because of disparities in cation radii, leading to a reduction in symmetry. Zero-phonon line (ZPL) emission of Mn4+ was observed in the low-temperature photoluminescent spectrum, confirming that Mn4+ ions occupy distorted octahedral sites. This ZPL merges the originally split emission peaks into a continuous broadband, significantly enhancing the spectral matching with the plant photosynthetically active radiation (PAR) spectrum. The optimal sample LAMT:0.008Mn4+ can achieve a high external quantum efficiency (EQE) of 37.6%. When the phosphor is encapsulated with a 365 nm LED chip, the resulting LED device exhibits an emission spectrum that is congruent with the absorption band of the plant phytochrome PFR, demonstrating the practical application prospects of this material in the field of plant lighting.