Effects of Al- and Sn-substitution on photoluminescence properties of Mn4+-doped spinel-type Mg2TiO4 phosphor

Solid solution phosphors in which the octahedral sites Mg2TiO4:Mn4+ were substituted by Al3+ and Sn4+ were synthesized and the relationship between the coordination environment of Mn4+ and the emission wavelength was investigated. Mn4+-doped Mg2TiO4-MgAl2O4 and Mg2TiO4-Mg2SnO4 red phosphors were prepared by a solid-state reaction. Mg2-xTi1-xAl2xO4:Mn4+ and Mg2Ti1-ySnyO4:Mn4+ were synthesized at 1400 °C and 1200 °C, respectively. The crystal structure parameters were refined using the RIETAN-FP program and the average bond lengths were calculated from the refined crystal structures of Mg2-xTi1-xAl2xO4:Mn4+ and Mg2Ti1-ySnyO4:Mn4+. The emission peak of the Al-substituted sample shifted toward shorter wavelengths with increasing Al concentration, whereas the emission peak of the Sn-substituted sample shifted toward longer wavelengths with increasing Sn concentration. In the 2E→4A2 transition, the emission peak wavelength of the Mn4+-activated spinel-type solid solution increased almost linearly with increasing average bond length between cation and anion in octahedral sites, Loct. These results indicate that there is a strong positive correlation between Loct and the emission peak wavelength for the solid solution compositions studied in this work.