Structure elucidation of BaSi 2O 2N 2 – A host lattice for rare-earth doped luminescent materials in phosphor-converted (pc)-LEDs

Abstract

BaSi 2O 2N 2 is a promising host lattice for rare-earth doped luminescent materials in phosphor-converted (pc)-LEDs. Applying a combined approach, its orthorhombic average structure (space group Cmcm (no. 63), a = 14.3902(3) Å, b = 5.3433(1) Å, c = 4.83256(7) Å and V = 371.58(2) Å 3, Z = 4) has been elucidated by electron diffraction and structure solution from X-ray and neutron powder diffraction data with subsequent Rietveld refinement ( wRp = 0.0491 for X-ray data). The structure contains layers of highly condensed SiON 3 tetrahedra with O terminally bound to Si. The Ba 2+ ions are situated between the layers and are surrounded by a cuboid of O atoms capped by two N atoms. In the structure, there is only one Ba site and one Si site, respectively, which is in accordance with a single sharp 29Si NMR signal observed at −52.8 ppm typical for SiON 3 tetrahedra in MSi 2O 2N 2 type oxonitridosilicates. Lattice energy calculations support the results of the structure determination.