Green route synthesis and optimized luminescence of K2SiF6:Mn4+ red phosphor for warm WLEDs

As the unique broadband blue light absorption and narrow-band red emission, the Mn4+-doped fluoride red phosphors have aroused tremendous attention for warm white light-emitting diodes (WLEDs). However, to prepare such phosphors, it is inevitable to use the hypertonic HF as solvent, which may be harmful to the environment. In our work, the K2SiF6:Mn4+ was prepared by using low toxicity (NH4F + HNO3/HAc/H3PO4) to replace HF. The structure, morphology and element composition have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometers (EDS) in detail, respectively. Upon 466 nm blue light excitation, the K2SiF6:Mn4+ can emit red light at near 632 nm. The influence of potassium sources and surfactants on luminescent properties of K2SiF6:Mn4+ were investigated. In addition, the concentration quenching mechanism was discussed. Moreover, the crystal field strength and emission mechanism of Mn4+ in K2SiF6 host were also analyzed. Finally, using K2SiF6:Mn4+ as red component, a warm WLED with low color temperature (CCT = 3816 K), high color rendering index (CRI, Ra = 87.7) and luminous efficiency (LE) of 139.51 lm/W was achieved, suggesting the K2SiF6:Mn4+ is an excellent red phosphor for warm WLEDs.