Review—The K<sub>2</sub>SiF<sub>6</sub>:Mn<sup>4+</sup> (PFS/KSF) Phosphor
W. E. Cohen, Fanghui Du, W.W. Beers, A.M. Srivastava
Abstract
In the modern-day phosphor-converted light emitting diodes (pc-LEDs), white-light for general illumination is generated by combiningblue light from the InGaN chip with the yellow-green emission of Ce doped garnet phosphor and a red emitter. The red emitter is required to induce a “warm-white” color temperature (2700–3500 K). The optical properties of the red emitter are critical to achieving high luminous efficacy (lumens per watt or LPW) and high color rendering index (CRI) of the white light. The red emitter must display both strong absorption at 450 nm and sharp line emission in the range of 610 nm − 650 nm. Currently, the red emitter that satisfies these requirements is the K 2 SiF 6 :Mn 4+ (PSF/KFS) phosphor. This review summarizes the fundamental aspects of the Mn 4+ ion luminescence in solids, the spectroscopic properties of the Mn 4+ ion in K 2 SiF 6 and the manufacturing procedures with particular emphasis on post-synthesis processes that are required to produce phosphor with acceptable reliability. The review also discusses alternate compositions, future improvements, and challenges.