Solution growth of millimeter‐scale Na2SiF6 single crystals for Mn4+‐doping as red phosphor

Abstract

AbstractThe cation exchange method has been demonstrated to be efficient in doping Mn4+ ions into various fluorides to synthesize the red‐emitting LED phosphors. This paper, however, reports the challenge in using this method to dope Mn4+ into the Na2SiF6 single crystals, to prepare the fluoride phosphor in single‐crystal form, a state‐of‐the‐art study in the white LED lighting field. The millimeter‐sized Na2SiF6 single crystals with a uniform columnar morphology (2–3 mm in length) were successfully grown in solution by a slow cooling process after optimizing the precursors. Then, the crystals were soaked in the HF solution dissolved with K2MnF6 to implement Mn4+‐doping via the cation exchange process. Evaluation of the Mn4+‐doping behavior reveals that the Mn4+ ↔ Si4+ cation exchange is less efficient in the case of single crystal host compared with the polycrystalline powdery ones and by‐reactions also occur which generates new phases. The Na2SiF6 single crystals doped with Mn4+ exhibit a series of discrete sharp peaks with intense zero phonon line emission at 617 nm under 450 nm blue irradiation. This study may trigger the exploration of new single crystal fluoride phosphor.