Hydrothermal synthesis and photoluminescence properties of red phosphor BaSiF6:Mn4+ for LED applications

An efficient red phosphor, BaSiF6:Mn4+ free of manganese oxide impurities, has been synthesized by using a one-step hydrothermal method at 120 degrees C for 12 h. The synthesis and chemical reactions have been investigated in detail and it includes: (a) influence of starting materials, concentrations of KMnO4 and HF, reaction temperature and time on products; (b) redox reaction of KMnO4 by HF; (c) chemical reaction mechanism for red phosphor BaSiF6:Mn4+center dot Mn4+ ions, acting as activators in the phosphor, originated from KMnO4 reduced by HF. The composition and crystal structure were determined with XRD, EDS and XPS. The morphology and thermal stability were investigated by SEM and TG-DSC, respectively. The maximum absorption band (at 460 nm) of the phosphor overlaps well with the blue emission of commercial InGaN LED. The room temperature emission spectrum of the phosphor shows a typical emission (centered at 632 nm) of Mn4+ in complex fluorides. The characteristic broad excitation band and sharp emission peaks of this red phosphor are desirable for potential applications as a red phosphor or for improving the color rendering index of conventional white LEDs.