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

The cation exchange method has been demonstrated to be efficient in doping Mn 4+ ions into various fluorides to synthesize the red-emitting LED phosphors. This paper, however, reports the challenge in using this method to dope Mn 4+ into the Na 2 SiF 6 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 Na 2 SiF 6 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 K 2 MnF 6 to implement Mn 4+ -doping via the cation exchange process. Evaluation of the Mn 4+ -doping behavior reveals that the Mn 4+ ↔ Si 4+ 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 Na 2 SiF 6 single crystals doped with Mn 4+ 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.