Mn4+ emission in pyrochlore oxides

Existing Mn4+ activated red phosphors have relatively low emission energies (or long emission wavelengths) and are therefore inefficient for general lighting. Density functional calculations are performed to study Mn4+ emission in rare-earth hafnate, zirconate, and stannate pyrochlore oxides (RE2Hf2O7, RE2Zr2O7, and RE2Sn2O7). The results show how the different sizes of the RE3+ cation in these pyrochlores affect the local structure of the distorted MnO6 octahedron, the Mn-O hybridization, and the Mn4+ emission energy. The Mn4+ emission energies of many pyrochlores are found to be higher than those currently known for Mn4+ doped oxides and should be closer to that of Y2O3:Eu3+ (the current commercial red phosphor for fluorescent lighting). The O-Mn-O bond angle distortion in a MnO6 octahedron is shown to play an important role in weakening Mn-O hybridization and consequently increasing the Mn4+ emission energy. This result shows that searching for materials that allow significant O-Mn-O bond angle distortion in a MnO6 octahedron is an effective approach to find new Mn4+ activated red phosphors with potential to replace the relatively expensive Y2O3:Eu3+ phosphor.