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

Abstract

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 D₃²-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 (∼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.