The Crystal Structure of Nitridomagnesogermanate Ba[Mg3GeN4]:Eu2+ and Theoretical Calculations of Its Electronic Properties

Nitridomagnesogermanate Ba[Mg3GeN4]:Eu2+ was synthesized by the NaN3 route in weld-shut tantalum ampules by reaction of the elements in molten sodium with NaN3 as nitrogen source at 780 degrees C. The crystal structure was solved and refined on the basis of single-crystal X-ray diffraction data. Ba[Mg3GeN4]:Eu2+ crystallizes in the UCr4C4 structure type [space group I4/m (no. 87), a = 8.3921(12), c = 3.4813(7) angstrom, Z = 2] and exhibits a highly condensed anionic network made up of statistically disordered (Mg/Ge)N-4 tetrahedra, which are connected to each other by common vertices and edges to form vierer ring channels along [001]. Ba2+ is located in every second channel and has cubelike coordination by eight N atoms. Theoretical calculations of the electronic properties of Ba[Mg3GeN4]:Eu2+ are discussed to understand the absence of photoluminescence in the visible range and for comparison with other luminescent materials that are structurally related to Ba[Mg3GeN4]:Eu2+.