Novel SrMg(2)La(2)W(2)O(12):Mn(4+) far-red phosphors with high quantum efficiency and thermal stability towards applications in indoor plant cultivation LEDs

Novel Mn(4+)-activated far-red emitting SrMg(2)La(2)W(2)O(12) (SMLW) phosphors were prepared by a conventional high-temperature solid-state reaction method. The SMLW:Mn(4+) 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(4+) doping concentration in the SMLW host was 0.2 mol% and the CIE chromaticity coordinates of SMLW:0.2% Mn(4+) 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(4+) ions were also investigated. Moreover, the internal quantum efficiency of SMLW:0.2% Mn(4+) 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(4+) far-red phosphors.