Synthesis and structure of the Na–Ba and Rb–Ba octagermanates and phosphorescence of the Rb2BaGe8-xO18:xMn4+ series

Structures of two new phases, Na2BaGe8O18 (1) and Rb2BaGe8O18 (2), were determined by single crystal X-ray diffraction. The phases are isostructural and crystallize with the P 3 ¯ c1 space group. The new octagermanates are built from the 3D anionic germanate frameworks, with alkali and alkaline earth cations located in their channels. The frameworks are made by corner-sharing GeO4 and GeO6 polyhedra. The way the GeOn polyhedra are connected in Na2BaGe8O18 (1) and Rb2BaGe8O18 (2) demonstrates a specific topology different from the related compounds. The patrial doping of the octahedral Ge sites in Rb2BaGe8O18 (2) with Mn4+ yielded a series of red-emitting phosphors. The photoluminescent data for these phosphors were collected and the highest phosphorescence intensity was found in the Rb2BaGe7.995O18: 0.005Mn4+ sample.