Synthesis of Mn4+ activated Na2SiF6 red-emitting phosphors using an ionic liquid

For the first time, the synthesis of Na2SiF6 powders was achieved through an ionothermal reaction using an ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate, without using toxic hydrogen fluoride (HF). Next, these powders were used as a host material to produce the red-emitting phosphor, Na2Si1-xMnxF6 (x = 0.007–0.200), that was synthesized using a low concentration HF solution with dissolved NaMnO4 as the Mn4+ source. The phosphors exhibited red-emission at 610 nm, 618 nm, 629 nm, and 644 nm from the 2Eg → 4A2g energy levels of Mn4+ under 460 nm excitation. The Na2SiF6 particles were non-agglomerated rod-shaped (~560 nm in length and ~230 nm in diameter), while the Na2Si1-xMnxF6 particles were spherically-shaped (~500 nm in diameter). Both of those powders were found to be much smaller than typical fluoride powders, which enables them to potentially improve the efficiency of phosphor-converted white-light-emitting diodes.