A novel red phosphor Cs 2 NaGaF 6 :Mn 4+ with ultra-strong zero-phonon lines and long wavelength phonon sidebands for high-quality WLEDs.

For high-efficiency lighting and wide color gamut backlight display, high-quality narrow-band red phosphors for WLEDs are still in high demand. Herein, a novel red-emitting fluoride phosphor Cs 2 NaGaF 6 :Mn 4+ was successfully synthesized by a simple two-step co-precipitation method and exhibits ultra-intense zero-phonon lines (ZPLs) and long wavelength phonon sidebands under 468 nm blue light irradiation. The ZPL emission peak of Cs 2 NaGaF 6 :Mn 4+ was located at 627 nm, which is much stronger than its υ 6 vibration peak, more matchable with the eye-sensitive region of humans, and beneficial for obtaining higher luminous efficiency of WLEDs. Interestingly, the υ 6 vibration peak of this red phosphor is at 636.5 nm, which is larger than that of the common fluoride phosphor A 2 BF 6 :Mn 4+ (usually at about 630 nm, represented by K 2 SiF 6 :Mn 4+ ) at about 6.5 nm. Thanks to the longer wavelength of the υ 6 vibration peak, the chromaticity coordinates (0.7026, 0.2910) with a larger x -coordinate value were realized, leading to a potentially wider color gamut of WLEDs. In addition, this phosphor has high thermal stability and its emission intensity at 423 K remains 93.7% of the initial intensity at room temperature. The lumen efficiency of WLED1 packaged with a mixture of Cs 2 NaGaF 6 :Mn 4+ and YAG:Ce 3+ on the InGaN blue chip is 115.7 lm W -1 with the color temperature ( T c ) = 3390 K and the colour rendering index ( R a ) = 92.5 under 20 mA driving current. The chromaticity coordinates of WLED2 packaged with Cs 2 NaGaF 6 :Mn 4+ and β-SiAlON:Eu 2+ on the InGaN blue chip are (0.3149, 0.3262) and the calculated color gamut is up to 118.4% (NTSC). These results indicate that Cs 2 NaGaF 6 :Mn 4+ red phosphors have promising applications in the high-quality lighting and display fields.