Novel Mn4+-activated LiLaMgWO6 far-red emitting phosphors: high photoluminescence efficiency, good thermal stability, and potential applications in plant cultivation LEDs

Double perovskite-based LiLaMgWO6:Mn4+ (LLMW:Mn4+) red phosphors were synthesized by traditional solid-state route under high temperature, and they showed bright far-red emission under excitation of 344 nm. The crystal structure, luminescence performance, internal quantum efficiency, fluorescence decay lifetimes, and thermal stability were investigated in detail. All samples exhibited far-red emissions around 713 nm due to the E-2(g) -> (4)A(2g) transition of Mn4+ under excitation of near-ultraviolet and blue light, and the optimal doping concentration of Mn4+ was about 0.7 mol%. The CIE chromaticity coordinates of the LLMW:0.7% Mn4+ sample were (0.7253, 0.2746), and they were located at the border of the chromaticity diagram, indicating that the phosphors had high color purity. Furthermore, the internal quantum efficiency of LLMW:0.7% Mn4+ phosphors reached up to 69.1%, which was relatively higher than those of the reported Mn4+-doped red phosphors. Moreover, the sample displayed good thermal stability; the emission intensity of LLMW:0.7% Mn4+ phosphors at 423 K was 49% of the initial value at 303 K, while the activation energy was 0.39 eV. Importantly, there was a broad spectral overlap between the emission band of LLMW:Mn4+ phosphors and the absorption band of phytochrome P-FR under near-ultraviolet light. All of these properties and phenomena illustrate that the LLMW:Mn4+ phosphors are potential far-red phosphors for applications in plant cultivation LEDs.