Novel luminescence enhancement and splitting of excitation and emission bands of Na2SiF6:Mn4+,Li+ phosphors induced by Li+ co-doping

Abstract

In this paper, a series of novel Na2SiF6:Mn4+,Li+ (NSF:0.05Mn4+, xLi+) phosphors were prepared with the cation exchange method. Some novel luminescent properties inducing by doping Li+ were observed: First, the striking thing is that the excitation (PLE) & emission (PL) intensities of Li+-doped sample (NSF:0.05Mn4+, 0.08Li+) are 11.7 times higher than those of NSF:0.05Mn4+; Second, when the concentration of Li+≥ 20%: (a) transition of 4A2g→4T2g in excitation band and zero phonon line (ZPL), s-v4 in emission band are all split into two peaks, respectively; (b) the peak intensities of as-v6, ZPL, v6 and v4 in emission band are almost the same. The mechanism of these phenomena was discussed. The color purity, crystal-field, nephelauxetic effect, the critical distance and the multipolar interaction for the samples were determined. Besides, the optimal sample (NSF:0.05Mn4+, 0.08Li+) has an excellent QY, which is as high as 99.83%. Good warm white light with low correlated color temperature (CCT = 4362 K) and high color rendering index (Ra = 88.5) was obtained from prototype WLEDs using the mixing phosphors of the optimal sample and YAG:Ce3+ on InGaN chip under a 20 mA drive current, making the optimal sample has potential application for blue light-based warm WLEDs.