Oxonitridosilicate Oxides REBa[SiON]O:Eu (RE = Y, Tb) with a Unique Layered Structure and Orange-Red Luminescence for RE = Y.

The oxonitridosilicate oxides REBa[SiON]O:Eu (RE = Y, Tb) were synthesized by high-temperature reaction in a radiofrequency furnace starting from REF, REO (RE = Y, Tb), BaH, Si(NH), and EuF. The structure elucidation is based on single-crystal X-ray data. The isotypic materials crystallize in the monoclinic space group Pm (no. 6) [Z = 3, a = 16.4285(8), b = 20.8423(9), c = 16.9257(8) Å, β = 119.006(3)° for RE = Y and a = 16.5465(7), b = 20.9328(9), c = 17.0038(7) Å, β = 119.103(2)° for RE = Tb]. The unique silicate layers are made up from Q-, Q-, and Q-type Si(O/N)- as well as Q-type SiN-tetrahedra, forming three slightly differing types of cages. The corresponding 3-fold superstructure as well as pronounced hexagonal pseudosymmetry complicated the structure elucidation. Rietveld refinement on powder X-ray diffraction data, energy-dispersive X-ray spectroscopy and infrared spectroscopy support the findings from single-crystal X-ray data. When excited with UV to blue light, YBa[SiON]O:Eu shows broad orange-red luminescence (λ = 628 nm, fwhm ≈ 125 nm/3130 cm). An optical band gap of 4.2 eV was determined for the doped compound by means of UV/vis spectroscopy.