Novel SrMgLaWO:Mn far-red phosphors with high quantum efficiency and thermal stability towards applications in indoor plant cultivation LEDs.

Novel Mn-activated far-red emitting SrMgLaWO (SMLW) phosphors were prepared by a conventional high-temperature solid-state reaction method. The SMLW:Mn phosphors showed a broad excitation band peaking at around 344 nm and 469 nm in the range of 300-550 nm. Under 344 nm near-ultraviolet light or 469 nm blue light, the phosphors exhibited a far-red emission band in the 650-780 nm range centered at about 708 nm. The optimal Mn doping concentration in the SMLW host was 0.2 mol% and the CIE chromaticity coordinates of SMLW:0.2% Mn phosphors were calculated to be (0.7322, 0.2678). In addition, the influences of crystal field strength and nephelauxetic effect on the emission energy of Mn ions were also investigated. Moreover, the internal quantum efficiency of SMLW:0.2% Mn phosphors reached as high as 88% and they also possessed good thermal stability. Specifically, the emission intensity at 423 K still maintained about 57.5% of the initial value at 303 K. Finally, a far-red light-emitting diode (LED) lamp was fabricated by using a 365 nm near-ultraviolet emitting LED chip combined with the as-obtained SMLW:0.2% Mn far-red phosphors.