Structural, electronic, and optical studies of BaRE2Ge3O10 (RE = Y, Sc, Gd–Lu) germanates with a special focus on the [Ge3O10]8− geometry

Abstract

A new series of BaRE₂Ge₃O₁₀ (RE = Y, Sc, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) trigermanates has been prepared using a solid-state reaction. Powder XRD study has revealed that the compounds crystallize in the monoclinic system, space group P2₁/m, Z = 2. The crystal lattice consists of edge-sharing REO₆ octahedra, bowed trigermanate [Ge₃O₁₀]⁸⁻ groups, and Ba atoms located in eight-fold coordinated irregular sites. The geometry of [Ge₃O₁₀]⁸⁻ anions persisting within different trigermanates has been examined with a special focus on the values of Ge–Ge–Ge angles and the types of conformation between the central and terminal GeO₄ tetrahedra. The arrangement of [Ge₃O₁₀]⁸⁻ anions in BaRE₂Ge₃O₁₀ (RE = Y, Sc, Gd–Lu) crystal lattices is found to be unique. DFT calculations of different polymorphs for BaY₂Ge₃O₁₀ and BaLa₂Ge₃O₁₀ compounds have confirmed that our fabrication protocol yields all the products in their most thermodynamically stable forms. According to the results of vibrational spectroscopy studies, diffuse reflectance and photoluminescence measurements, the BaRE₂Ge₃O₁₀ trigermanates are promising compounds for the preparation of efficient lanthanide ion activated phosphors.