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

Abstract

A one-step approach to synthesize Na ₂SiF ₆:Mn ⁴⁺and K ₂SiF ₆:Mn ⁴⁺ red phosphors by co-precipitation is reported in this paper.

Abstract

A one-step approach to synthesize Na ₂SiF ₆:Mn ⁴⁺and K ₂SiF ₆:Mn ⁴⁺ red phosphors by co-precipitation is reported in this paper. The phosphors were precipitated from a silicon fluoride solution with NaF and Na ₂MnO ₄ (Na ₂SiF ₆:Mn ⁴⁺ preparation) or KF and K ₂MnO ₄ (K ₂SiF ₆:Mn ⁴⁺ preparation) using H ₂O ₂ to reduce Mn ⁷⁺ to Mn ⁴⁺ at room temperature. Na ₂SiF ₆:Mn ⁴⁺ was also prepared through a convenient two-step route with K ₂MnF ₆ as a raw material. The obtained Na ₂SiF ₆:Mn ⁴⁺ 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 (∼92% of the luminescent intensity at 423 K). Increasing the concentration of Mn ⁴⁺ enhanced the luminescence intensity. A warm white light LED with high color rendering index ( R _a = 86 and R9 = 61) was fabricated by employing Na ₂SiF ₆:Mn ⁴⁺ as red phosphors and commercial Y ₃Al ₅O ₁₂:Ce ³⁺ as yellow phosphors on a blue-InGaN chip.