A red phosphor of Ba3In2F12:Mn4+ with enhanced moisture stability for warm WLED application

Although fluoride phosphors have distinguishing feature in luminescence spectra such as narrow band red light emission and broad band blue light excitation, the instability of [MnF6]2- limits their commercial applications. In this regard, we use weak reducing agents such as citric acid (CA) and oxalic acid (OA) for surface modification of a novel red phosphor Ba3In2F12:Mn4+ (BIF:Mn). A protective homogeneous passivation layer is formed on the surface of the phosphor particles with reduced Mn4+ content to improve the moisture resistance of Mn4+ doped fluoride phosphor BIF:Mn. In addition, their crystal structures, morphologies, photoluminescence characteristics, and the mechanism of luminescence enhancement are also described in details. By using near-ultraviolet or blue light-emitting diodes (LEDs) to excite it, an efficient red emission has been achieved with a maximum peak at 631 nm. In order to verify their application value, a warm white LED (WLED) with a color rendering index (CRI = 81.4) and a correlated color temperature (CCT = 4779 K) has fabricated with the as-prepared BIF:Mn and commercial yellow phosphor (YAG:Ce) on blue GaInN chip.