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

Abstract

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 E-2(g)->(4)A(2g) energy levels of Mn4+ under 460 nm excitation. The Na2SiF6 particles were non-agglomerated rod-shaped (similar to 560 nm in length and similar to 230 nm in diameter), while the Na2Si1-xMnxF6 particles were spherically-shaped (similar to 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.