A rare-earth free red-emitting MgO-MgF2-GeO2:Mn4+ phosphors were synthesized and optimized for maximal luminescent intensity by the solid-state reaction. The excitation spectrum consists of two broad bands due to the Mn4+ ion, covering the wavelength range from 250~480 nm. The main peak of the excitation band is located at 420 nm. It provides pure red light, which is of 658 nm wavelength with narrow full-width at half-maximum of 15 nm upon 420 nm excitation. The luminescence intensity of 3.5MgO·0.5MgF2·GeO2:Mn4+ could be enhanced by choosing proper flux of SrF2, in particular. The 3.5MgO·0.5MgF2·GeO2:Mn4+ exhibits the Commission International de I'Eclairage (CIE) chromaticity coordinates of (0.7154, 0.2846). The white LED was fabricated by blending two phosphors of 3.5MgO·0.5MgF2·GeO2:Mn4+ and β- SiAlON : Eu2+ (green emitting phosphor) on the 420 nm emitting UV-chip as well as 450 nm emitting blue chip. Usual Color Rendering Index (CRI), i.e., the mean value of CRIs from R1 to R8, is 84.9 and its color gamut could be extended by 126.4%, comparing to sRGB.

Keywords: Phosphor, LED, Mn4+, FWHM.