Abstract

The new group of optical materials, so called calcium and manganese rare-earth tetrametagermanates Ln₂M²⁺Ge₄O₁₂, Ln = Eu – Lu or Y, M²⁺ = Ca, Mn, and solid solutions Er_xY_2-xCaGe₄O₁₂, Pr_xY_2-xMnGe₄O₁₂, 0 ≤ x ≤ 2, were synthesized and their crystal and optical properties were investigated. All compounds are isostructural and their crystal structure belongs to the space group P4/nbm (No. 125, Z = 2). The existence of cyclic anions [Ge₄O₁₂]⁸⁻, consisting of four GeO₄ tetrahedra, is the main feature of the crystal structure which consists of two alternating layers. The first layer type includes [Ge₄O₁₂]⁸⁻ anions in boat-type conformation. Between these layers octahedral and square antiprismatic cavities are formed, that are occupied by Ln and (Ca, Mn) atoms of the second layer type. Values of interatomic distances and bond angles inside cyclic anion groups [Ge₄O₁₂]⁸⁻ are nearly equal in all compounds. So the structure of tetracycles is rigid. The L n and (Ca, Mn) atoms are placed inside elongated oxygen octahedrons with ratio 0.5/0.5. The square antiprisms are occupied only by rare-earth cations. The decreasing atomic radius of the rare earth elements leads to a change of the island structure motive to the 2D layered type.

© 2009 IEEE