A series of Mn⁴⁺-activated CaLaMgSbO₆ far-red-emitting phosphors were synthesized by a solid-state reaction route and the microstructure and optical characterizations were investigated in detail. Upon excitation at 370 and 469 nm, the samples showed intense far-red emission at about 708 nm originating from the ²E_g → ⁴A_2g transition and the optimal Mn⁴⁺ concentration was 0.7 mol%. The as-prepared phosphors also exhibited excellent internal quantum efficiency (88%) and high thermal stability. The emission intensity at room temperature dropped to 54% when the temperature rose to 423 K and the activation energy was 0.34 eV. The outstanding optical properties and the fact that the emission band of the obtained phosphors had a broad overlap with the absorption band of phytochrome P_FR demonstrated that the CaLaMgSbO₆:Mn⁴⁺ phosphors may be promising potential spectral converters for applying to indoor plant cultivation light-emitting diodes.