Comparative analysis on the photoluminescence properties of Cs2BF6:Mn4+ (B = Ge, Si, Zr, Ti) red phosphors for WLEDs

A series of Cs2BF6:Mn4+ (B = Ge, Si, Ti, Zr) red phosphors were synthesized by a precipitation-cation exchange route. The phase purity, morphology, and constituent were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Optical properties were investigated by photoluminescence (PL) spectra and high-resolution PL. Temperature-dependent PL examination at the range of both 273-573 K and 10-300 K was performed to investigate the emission mechanism of Mn4+ in these fluorides. The intensity for both zero-phonon lines (ZPLs) and vibration coupled emission of Mn4+ in these four systems with different crystal structures was investigated systematically. These phosphors present bright red emission under blue light (467 nm) illumination, among which Cs2GeF6:0.1Mn(4+) shows the highest emission intensity with ultrahigh quantum efficiency of 94%. The white light-emitting diodes (WLEDs) fabricated with this sample, blue InGaN chips and commercial YAG:Ce3+ phosphor exhibited high luminous efficacy beyond 100 lm/w with high color rendering index (similar to 88.6) and low color temperature (similar to 3684 K).