REBa[SiONC]:Eu ( RE = Lu, Y): Green-Yellow Emitting Oxonitridocarbidosilicates with a Highly Condensed Network Structure Unraveled through Synchrotron Microdiffraction.

The oxonitridocarbidosilicates REBa[SiONC]:Eu ( RE = Lu, Y) were synthesized by carbothermal reactions starting from REO, graphite, BaSiN, Si(NH), and EuO. The crystal structure of LuBa[SiONC]:Eu was elucidated on a submicron-sized single crystal by a combination of transmission electron microscopy and microfocused synchrotron radiation. The compound crystallizes in trigonal space group P3 (no. 143) with a = 16.297(4) Å, c = 6.001(2) Å, and Z = 3 ( R1 = 0.0332, wR2 = 0.0834, GoF = 1.034). According to Rietveld refinements on powder X-ray diffraction data, YBa[SiONC]:Eu is isotypic with a = 16.41190(6) Å and c = 6.03909(3) Å. The crystal structures are built up of vertex-sharing SiC(O/N) tetrahedra forming star-shaped units [C(Si(O/N))] with carbon atoms in fourfold bridging positions. Energy-dispersive X-ray spectroscopy and CHNS analysis correspond to the sum formula, lattice energy, and charge distribution calculations support the assignment of O/N/C atoms. When excited with UV to blue light, Eu-doped samples show green luminescence for RE = Lu (λ ≈ 538 nm, full width at half-maximum (fwhm) ≈ 3600 cm) and yellow emission in the case of RE = Y (λ ≈ 556 nm, fwhm ≈ 4085 cm).