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

Abstract

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 photo-luminescence 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.