Synthesis and photoluminescence properties of octahedral K2(Ge,Si)F6:Mn4+ red phosphor for white LED

Abstract A novel red-emitting K 2 (Ge,Si)F 6 :Mn 4+ phosphor with uniform morphology was synthesized by co-precipitation method. The pure K 2 GeF 6 phase with P 6 3 mc space group other than P 3 m 1 space group was affirmed just by incorporation of Si in K 2 GeF 6 at room temperature according to XRD characterization. SEM images showed lamellar and octahedron grain morphology for K 2 GeF 6 :Mn 4+ and K 2 (Ge,Si)F 6 :Mn 4+ phosphors, respectively. It was also found that the photoluminescence excitation (PLE) and photoluminescence (PL) showed slight displacement in K 2 GeF 6 :Mn 4+ and K 2 (Ge,Si)F 6 :Mn 4+ system. And the zero-phonon line (ZPL) of the PL spectrum of K 2 GeF 6 :Mn 4+ with Si showed a strong peak. Meanwhile crystalline field surrounding Mn 4+ changes could affect the decay time in this fluoride system. The color gamut of the LED devices based on K 2 (Ge,Si)F 6 :Mn 4+ and K 2 GeF 6 :Mn 4+ reached up to 94.58% NTSC (National Television Standards Committee) and 94.386% NTSC, respectively, that was much higher than that based on nitride red phosphors. All these original characteristics in K 2 (Ge,Si)F 6 :Mn 4+ phosphor are desirable for potential applications as a red phosphor for improving lighting and display quality of conventional white LEDs.