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

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.