Highly efficient red phosphor Cs2GeF6:Mn4+ for warm white light-emitting diodes

Red phosphor Cs2GeF6:Mn4+ has been synthesized by the cation exchange method. The as-prepared phosphor was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectrometer (EDS), atomic absorption spectrophotometer (AAS), thermogravimetry (TG) and differential scanning calorimetry (DSC). Its optical properties were investigated by photoluminescence spectra (PL), diffuse reflectance spectra (DRS), the low-temperature emission spectrum and the luminescence decay curve. The sample doped with 8.78 mol% Mn4+ exhibits an intense red emission with a high thermal stability and appropriate CIE coordinates (x = 0.69, y = 0.31), and its emission intensity is higher than that of commercial K2TiF6:Mn4+. The white light-emitting diodes (WLEDs) fabricated with this sample exhibit intense warm white-light with a low color temperature (T-c = 3673 K), high color rendering index (R-a = 84.9) and high luminous efficacy (LE = 141.5 lm W-1). So Cs2GeF6:Mn4+ may be a promising red component for warm WLEDs.