The　advent　of　wide　color-gamut　LED　backlight　technology　greatly　improves　the　user　experience　in　visions.　The　bottleneck　restricting　progress　of　this　technology　is　to　develop　red　phosphor　with　satisfactory　spectral　features　and　low　cost.　Herein,　a　novel　non-rare-earth　K2XF7:　Mn4+　(X　=　Ta,　Nb)　was　successfully　designed　and　synthesized,　exhibiting　an　admirable　quantum　efficiency　of　similar　to　93.5%,　an　extremely　narrow　FWHM　of　similar　to　2.3　nm,　and　a　high　color　purity　of　similar　to　99.6%.　Unlike　the　previously　reported　Mn4+　activated　fluorides,　Mn4+　in　K2XF7　suffers　highly　distorted　octahedral　environment　in　C-1　(or　C(2)v)　group　symmetry,　enabling　the　appearance　of　intense　zero　phonon　line　and　distinctive　vibronic　transitions.　Systematical　high-resolution　spectroscopic　analyses　down　to　10　K　disclose　the　influences　of　strong　crystal　field,　weak　nephelauxetic　effect,　and　intermediate　electron-phonon　coupling　are　responsible　for　the　peculiar　spectral　features　of　Mn4+　in　K2XF7.　Impressively,　a　wide　color-gamut　reaching　up　to　86.7%　NTSC　is　realized,　demonstrating　great　validity　of　K2XF7:Mn4+　for　LCD　backlights.　The　present　study　not　only　brings　a　brand-new　kind　of　Mn4+　activated　host　to　the　sight　of　phosphor　community　(the　host　can　be　extended　to　surges　of　tantalum/niobium　fluorides),　but　also　may　enlighten　researchers　to　design　highly　distorted　environment　to　achieve　unique　spectral　properties　of　Mn4+.