Structure elucidation of BaSi2O2N2 - A host lattice for rare-earth doped luminescent materials in phosphor-converted (pc)-LEDs

BaSi2O2N2 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) angstrom, b = 5.3433(1) angstrom, c =4.83256(7) angstrom and V= 371.58(2) angstrom(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 SiON3 tetrahedra with O terminally bound to Si. The Ba2+ 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 Si-29 NMR signal observed at -52.8 ppm typical for SiON3 tetrahedra in MSi2O2N2 type oxonitridosilicates. Lattice energy calculations support the results of the structure determination. (c) 2008 Elsevier Masson SAS. All rights reserved.