Room-temperature synthesis, optimized photoluminescence and warm-white LED application of a highly efficient non-rare-earth red phosphor

Non-rare-earth red phosphors as alternative to commercial (oxy) nitride phosphors have attracted considerable attention for energy-efficient warm white light-emitting diodes (WLEDs). An excellent narrow-band red emission K2GeF6:Mn4+ product was successfully obtained through co-precipitation method. The crystal structure, morphology, composition and optical properties of K2GeF6:Mn4+ samples were investigated in details via X-ray powder diffraction (XRD), field emission scanning electron microscope (FESEM), energy dispersive spectrometry (EDS) and photoluminescence spectra, respectively. Mn4+ activated K2GeF6 red phosphor possesses two strong and wide absorption bands in the region of 300–500 nm, which can be applied to UV and blue LED chips and bright intense red light (635 nm) with high color purity. Simultaneously, mechanisms of concentration and temperature quenching were systematically elucidated. After a systematic investigation, the luminescence properties of K2GeF6:Mn4+ have been optimized by changing synthetic conditions, such as the doping concentration, the concentration of HF, the potassium source, the amount of KF and the addition of surfactant. The red phosphor K2GeF6:Mn4+ was packaged via mixing commercial YAG:Ce yellow phosphor, an outstanding warm WLED with low CCT (3882 K), high CRI (Ra = 90.4) and high luminous efficacy (LE) of 125.84 lm/W has been obtained, implying that K2GeF6:Mn4+ is the potential red phosphor for warm WLEDs.