Bredigite-structure Ca14Mg2[SiO4]8:Eu2+,Mn2+: A tunable green–red-emitting phosphor with efficient energy transfer for solid-state lighting

A single-phase green–red-emitting phosphor, Ca13.7Eu0.3Mg2−xMnx[SiO4]8 (CMS:Eu2+,Mn2+), was prepared by a solid-state reaction, and its energy transfer from Eu2+ to Mn2+ was investigated as a function of Mn2+ concentration. To explore the substitution of an Mn2+ site for each Mg site, a determination of the number of Mg substitutional sites was carried out using the Rietveld refinement method and bond valence sums. The dipole–dipole interaction was a dominant energy transfer mechanism of the electric multipolar character of CMS:Eu2+,Mn2+. The critical distance was calculated as 7.5 Å when using critical concentrations of Eu2+ and Mn2+. When CMS:Eu2+,Mn2+ was incorporated with an encapsulant in ultraviolet (λmax = 400 nm) light-emitting diodes (LEDs), white light with a color rendering index of 67 under a forward bias current of 20 mA was obtained. The results of this work indicate that CMS:Eu2+,Mn2+ could be applicable to a single-phase phosphor for white LEDs under a near-ultraviolet source.