Hydrothermal synthesis, morphology and photoluminescent properties of an Mn4+-doped novel red fluoride phosphor elpasolite K2LiAlF6

Presently, new red emitting Mn4+ activated fluoride phosphors that are obtained via green synthetic routes remain a great challenge in the field of luminescent materials for advanced applications in solid state lighting and displays. In this study, for the first time, we develop a novel red emitting fluoride phosphor, K2LiAlF6: Mn4+, and it is synthesized in low-toxic H3PO4/KHF2 liquid instead of the highly toxic HF liquid, which is a necessity in the synthesis of fluoride phosphors. Moreover, the morphology and photoluminescence properties of K2LiAlF6: Mn4+ were systematically investigated. The results show that the Mn4+ ion exhibits a broadband excitation extending from 300 to 500 nm, which matches well with UV and blue LED chips and obtains an ideal red emission at 635 nm, due to the similarities in cation site symmetry and host iconicity between the famous K2TiF6 and target K2LiAlF6. Moreover, K2LiAlF6: Mn4+ has an excellent thermal quenching behavior and color stability in the temperature range of 300-500 K, compared with the commercial red nitride phosphor (Sr) CaAlSiN3: Eu2+.