K2MnF5·H2O as reactant for synthesizing highly efficient red emitting K2TiF6:Mn4+ phosphors by a modified cation exchange approach

As reactant for synthesizing K2TiF6:Mn4+ phosphors, the cross-shaped and cuboid-shaped K2MnF5·H2O powders were prepared by the simple chemical method. Based on the reaction mechanism, oxidizing K2MnF5·H2O (Mn3+) to Mn4+ by KMnO4 (Mn7+), a modified cation exchange approach for synthesizing highly efficient red emitting K2TiF6:Mn4+ phosphor was proposed. The obtained K2TiF6:Mn4+ (2.7-5.3 at.%) phosphors have the size of 30-80 μm with a rough surface, their emission spectra consist of five narrow bands extending from 580 to 660 nm with the strongest peak at 634.8 nm, whose relative emitting intensity depends on the molar ratio of KMnO4 to K2MnF5·H2O (the platform value = 3.2), and two broad excitation bands are peaking at ∼365 nm and ∼460 nm. The internal quantum yield of our synthesized K2TiF6:Mn4+ phosphors is up to 82.5%, which is higher than the commercial CaAlSiN3:Eu2+ value, their excitation bands peak at ∼460 and ∼365 nm are consistent with those of Y3A5O12:Ce3+ phosphors and their emission bands are more suitable for the sensitivity curve of photopic human vision. In addition, our synthesized phosphors show better thermal quenching properties. These findings show a large potential of the synthesized K2TiF6:Mn4+ phosphors for commercialization.