HF-Free Hydrothermal Route for Synthesis of Highly Efficient Narrow-Band Red Emitting Phosphor K₂Si_1–<i>x</i>F₆:<i>x</i>Mn⁴⁺ for Warm White Light-Emitting Diodes

With superior photoluminescent properties, the recently discovered A2MF6:Mn4+ material holds the potential in replacing the commercial rare-earth-doped (oxy)nitride phosphors for solid state lighting and display. We report here a green synthetic route to synthesize narrow red emitting K2SiF6:Mn4+ without the usage of toxic and volatile HF solution. We show that K2SiF6:Mn4+ is produced in common low-toxic H3PO4/KHF2 liquid instead of high-toxic HF liquid and systematically investigate its morphology and photoluminescence properties. Moreover, the reaction mechanism is comprehensively discussed in detail. We find that not only does H3PO4/KHF2 play the same key roles as HF in the process of stabilizing Mn4+ and promoting Mn4+ into the host K2SiF6, but also it exhibits more excellent ability than HF in controlling the concentration of Mn4+ ion in the host K2SiF6. By demonstrating its application in white light-emitting diode (LED) with tunable chromaticity coordinate and correlated color temperature, we show that our hydrothermal strategy based on low-toxic H3PO4/KHF2 solution system will open the opportunity for the narrow red emitting A2MF6:Mn4+ to be synthesized in large scale toward white LED industry adoptions.