A novel Mn4+-activated garnet-type Li5La3Nb2O12 far red-emitting phosphor with high thermal stability for plant cultivation

Abstract Far-red phosphors Li5La3Nb2O12 (LLNO):Mn4+ were synthesized by solid-state reaction and the luminescent properties of the phosphors were studied in detail. LLNO:Mn4+ phosphors exhibit far-red emission band from 650 to 760 nm under near-ultraviolet excitation at 318 nm. Due to the Mn4+: 2Eg→4A2g transition, the broad emission band centered at 715 nm matched well with the absorption wavelength range of plant phytochrome PFR (710–740 nm). Furthermore, typical concentration quenching occurs when the doping concentration of Mn4+ exceeds 2% due to dipole-dipole (d-d) interaction. Impressively, for LLNO:0.002Mn4+ phosphors, the emission intensity of 423 K (150 °C) is about 79.2% of that of 298 K (25 °C), and the corresponding activation energy is 0.4339 eV, indicating that the material exhibits excellent thermal stability. Finally, all the chromaticity coordinates of LLNO:Mn4+ located at far-red region. The conclusions drawn above indicate that LLNO:Mn4+ far-red phosphors have potential application value in the field of plant lighting.