Mn-doped LiNaGe₄O₉ as a rare-earth free phosphor: Impact of Na-substitution on emission in tetragermanate phase

We have synthesized Mn⁴⁺-doped mixed tetragermanate phases in the Li₂Ge₄O₉LiNaGe₄O₉ system, i.e., Li(Li,Na)Ge₄O₉, by a glass-ceramic technique using stoichiometric precursor glasses, and have examined the effect of substitution of Na on their photoluminescence properties. The tetragermanate phases indicated clear red emission based on a ²E→⁴A₂ transition, and the entire substitution resulting in an LiNaGe₄O₉ phase provided an improvement of quenching temperature for the emission. Furthermore, the LiNaGe₄O₉ phase synthesized by solid-state reaction showed a high internal quantum yield and red color purity, demonstrating it to be a possible candidate as a rare-earth-free red phosphor.