Europium Lithosilicates Li2EuSi2N4 and Li2EuSiO4-Crystal Structures and Luminescence.

Abstract

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) Å3. Irradiated with blue light, Li2EuSi2N4 exhibits a narrow-band red emission (λmax = 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 (λmax = 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.