Enhanced chromaticity and dual emission in double-site Mn4+-activated KLiTiF6 red phosphors for wide color gamut displays

Abstract

Mn⁴⁺-activated fluoride phosphors are pivotal for white LEDs due to their narrow-band red emission, which is essential for achieving wide color gamut displays. A red shift in the emission spectrum, especially with a chromaticity coordinate x value larger than 0.70, is essential for enhancing the color gamut. However, suitable narrow-band red-emitting phosphors that meet this requirement are currently very limited in reported studies. In this study, we report the design and synthesis of a novel red-emitting phosphor, KLiTiF₆:Mn⁴⁺ (KLTFM), which exhibits strong red emission under blue light excitation. The synthesized KLTFM phosphor features distinct zero-phonon lines at 620 nm and 622 nm, confirming the presence of two unique Mn⁴⁺ luminescence centers within the KLiTiF₆ host. Additionally, KLTFM exhibits a primary emission peak at 632 nm, with chromaticity coordinates of (0.70, 0.31), surpassing the chromaticity of commercial red phosphor K₂SiF₆:Mn⁴⁺ with primary emission at 630 nm and coordinates of (0.69, 0.30), thus demonstrating a significant red shift. White LEDs fabricated with KLTFM phosphors achieved a correlated color temperature (CCT) of 9961 K, a luminous efficacy of 91.60 lm W⁻¹, a 116.1% color gamut relative to the NTSC standard, and an 86.7% color gamut coverage of the Rec.2020 standard, representing a 2.02% and 5.99% improvement over the K₂SiF₆:Mn⁴⁺-based prototype, respectively. These results underscore the potential of KLTFM red phosphors in enhancing wide color gamut white LEDs, particularly for LCD backlight display applications requiring wide color gamut coverage.