Far-red emitting Mn4+-Activated Ca2AlTaO6 double perovskite for plant growth lighting

A series of Mn 4+ -doped monoclinic double perovskite Ca 2 AlTaO 6 (CAT:Mn 4+ ) far-red-emitting luminescent materials were successfully synthesized via a high-temperature solid-state reaction route. The crystal structure, luminescence properties, concentration quenching mechanism, thermal stability and application potential for plant growth lighting were systematically investigated. All as-prepared samples present a pure monoclinic structure with space group P2 1 /n, and Mn 4+ ions are successfully incorporated into the lattice by substituting Ta 5+ sites without any impurity phases. Under 360 nm near-ultraviolet excitation, CAT:Mn 4+ exhibits intense far-red emission centered at 710 nm, originating from the characteristic 2 E→ 4 A 2 transition of octahedrally coordinated Mn 4+ . The optimal doping concentration of Mn 4+ is determined to be x = 0.006, and the concentration quenching is dominated by electric dipole-dipole interactions with a critical quenching distance of 26.1 Å. The internal quantum efficiency of the optimal sample reaches 34%. Biexponential decay analysis shows that the average luminescence lifetime rises monotonically with increasing Mn 4+ doping concentration. This behavior originates from competing effects: defect suppression dominates at low dopant contents, whereas concentration-dependent quenching takes over at higher doping levels. The activation energy for thermal quenching is calculated to be 0.305 eV, and the sample retains 20% of its initial emission intensity at 423 K, exhibiting moderate thermal stability. The prototype near-ultraviolet-excited device based on CAT:0.006Mn 4+ presents good luminescent efficiency and satisfactory spectral stability under variable driving currents. This work demonstrates that CAT:Mn 4+ is a promising far-red luminescent candidate for plant growth lighting applications.