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

Abstract

An efficient red phosphor, BaSiF₆:Mn⁴⁺ free of manganese oxide impurities, has been synthesized by using a one-step hydrothermal method at 120 °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⁺. 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.