Europium Lithosilicates Li₂EuSi₂N₄ and Li₂EuSiO₄-Crystal Structures and Luminescence

With Li₂EuSi₂N₄, the end member of the solid-solution series set up by substituting the divalent cation in the well-known host materials Li₂CaSi₂N₄ and Li₂SrSi₂N₄ with Eu(II) could be synthesized and described by means of single-crystal X-ray diffraction and single-grain luminescence spectroscopy. The new compound crystallizes isotypically to Li₂CaSi₂N₄ and Li₂SrSi₂N₄ in cubic space group Pa3̅ (no. 205) with a lattice parameter of a = 10.7049(2) Å and a cell volume of V = 1226.73(7) ų. Irradiated with blue light, Li₂EuSi₂N₄ exhibits a narrow-band red emission (λ_max = 628 nm, 1.97 eV, 15924 cm^-1; fwhm = 83 nm, 0.27 eV, 2143 cm^-1). Also for Li₂EuSiO₄, the end member of the solid-solution series of Li₂SrSiO₄ with Sr(II) substituted by Eu(II), luminescence emission could be measured on a single crystal (λ_max = 595 nm, 2.05 eV, 16798 cm^-1; fwhm = 116 nm, 0.40 eV, 3211 cm^-1). In this paper, both compounds are being compared with other known members of their solid-solution series regarding structure and luminescence properties.