Crystal field optimization, luminescence enhancement and thermal stability of novel K2NaAl0.4Ga0.6F6:Mn4+ solid solution red phosphor for high-performance warm WLED

Mn 4+ -doped fluoride phosphors have important application value in the background light and WLED lighting fields. Therefore, the synthesis of efficient and stable Mn 4+ -doped red phosphor is of great application value. In this study, a series of red-emitting K 2 NaAl 1- y Ga y F 6 : x Mn 4+ ( y = 0, 0.2, 0.4, 0.6, 0.8 and 1) ( x = 0.01, 0.03, 0.05, 0.07 and 0.09) solid solution phosphors are successfully synthesized by simple coprecipitation method. The synthesis strategy of simple crystal structure optimization is proposed to realize simultaneously the crystal field optimization, luminescence enhancement and thermal stability of red phosphor. The calculation and theoretical analysis of crystal field strength are used to prove that solid solution matrix K 2 NaAl 0.4 Ga 0.6 F 6 is the most ideal matrix material. X-ray powder diffraction, energy-dispersive X-ray spectrometer and scanning electron microscope are employed to determine the crystal structure, composition and morphology of all samples. Optical properties are characterized using excitation spectra, emission spectra and fluorescence lifetime curves. Moreover, the CIE coordinates of red-light show that the phosphor has low correlated color temperature and excellent color purity. Intriguingly, the as-prepared K 2 NaAl 0.4 Ga 0.6 F 6 :Mn 4+ phosphor possesses admirable thermal quenching behavior and color stability at high temperature. At a temperature of 423 K, the photoluminescence intensity can be maintained at 52 % of the original intensity (298 K). The activation energy, the chromaticity shift and chromaticity coordinate variation are also systematically calculated. More importantly, A high-performance warm WLED with low correlated color temperature (CCT = 3982 K) and high color rendering index (R a = 93.7) is achieved by using K 2 NaAl 0.4 Ga 0.6 F 6 :Mn 4+ as a red-emitting material. These results demonstrate that K 2 NaAl 0.4 Ga 0.6 F 6 :Mn 4+ red phosphor provides a novel choice for the warm WLED required for indoor lighting.