Structure elucidation of BaSi_2O_2N_2 - A host lattice for rare-earth doped luminescent materials in phosphor-converted (pc)-LEDs

摘要

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) A, b = 5.3433(1) A, c = 4.83256(7) A and V= 371.58(2) A~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 0 terminally bound to Si. The Ba~(2+) ions are situated between the layers and are surrounded by a cuboid of 0 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 ~(29)Si 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.