Double perovskite La2LiNb(1-)O6: xMn4+ red phosphors with excellent humidity stability and high thermal stability for plant growth LEDs

In recent times, there has been significant interest in Mn4+-activated red phosphors in double perovskite oxide materials. However, the practical use of these materials is hindered by concerns related to their thermal and humidity stability. In this research, we have synthesized deep red-emitting phosphors with the composition La2LiNb(1-x)O6: xMn4+ using a conventional high-temperature solid-phase method. The microstructures and luminescence properties of these phosphors have been thoroughly investigated. All the samples consist of irregular microcrystals with an average size ranging from 3 to 7 μm, and they exhibit excellent phase purity and crystallinity. Under excitation by 335 nm ultraviolet light, the La2LiNb(1-x)O6:xMn4+ phosphors emit a narrow and sharp red band (centered at ∼710 nm), and the emission intensity initially increases and then decreases with increasing Mn4+-doping concentration, peaking at x = 0.5%. The La2LiNb0.995O6: 0.5%Mn4+ phosphor exhibits exceptional thermal stability, with a normalized emission intensity of 66.24% maintained at 150 °C. More importantly, the La2LiNb0.995O6:0.5%Mn4+ phosphor exhibits excellent humidity stability and can maintain more than 90% of its initial emission intensity after immersion in deionized water for 24 h. The La2LiNb0.995O6: 0.5%Mn4+ phosphor demonstrates an impressive resistance to humidity-induced luminescence quenching. It maintains a significantly higher far-red emission intensity at relative humidities exceeding 65%. These newly developed La2LiNb(1-x)O6: xMn4+ phosphors hold great potential as red phosphors for high-power plant growth LEDs in extended outdoor, high-humidity conditions.