Synthesis of Na2SiF6:Mn4+ red phosphors for white LED applications by co-precipitation

A one-step approach to synthesize Na2SiF6:Mn4+ and K2SiF6:Mn4+ red phosphors by co-precipitation is reported in this paper. The phosphors were precipitated from a silicon fluoride solution with NaF and Na2MnO4 (Na2SiF6:Mn4+ preparation) or KF and K2MnO4 (K2SiF6:Mn4+ preparation) using H2O2 to reduce Mn7+ to Mn4+ at room temperature. Na2SiF6:Mn4+ was also prepared through a convenient two-step route with K2MnF6 as a raw material. The obtained Na2SiF6:Mn4+ phosphors have hexagonal structures with space group D-3(2)-P321 and no impurity phase when they were examined via X-ray diffraction. Photoluminescence, photoluminescence excitation, thermal luminescence, and luminescence decay time were considered to determine the optical properties of the fluoride complexes. The prepared phosphors exhibited bright red emission under 460 nm light excitation and low-thermal quenching (similar to 92% of the luminescent intensity at 423 K). Increasing the concentration of Mn4+ enhanced the luminescence intensity. A warm white light LED with high color rendering index (R-a = 86 and R9 = 61) was fabricated by employing Na2SiF6:Mn4+ as red phosphors and commercial Y3Al5O12:Ce3+ as yellow phosphors on a blue-InGaN chip.