Synthesis, crystal structure, magnetic and luminescence properties of KEuGe₂O₆: A europium cyclogermanate containing infinite chains of edge-sharing Eu-O polyhedra

A new Eu(III) germanate, KEuGe₂O₆, has been synthesized by both the flux-growth method and the high-temperature, high-pressure hydrothermal method and characterized by single-crystal X-ray diffraction. The compound contains parallel zigzag chains of edge-sharing Eu-O polyhedra, which are in turn linked by sharing vertices and edges with three-membered single ring Ge₃O₉^6- germanate anions to form a 3-D framework structure. The magnetic and luminescence properties were also investigated. The observed χ_MT value at 300 K is 4.53 emu K mol^-1, which is in good agreement with the calculated value for three Eu³⁺ ions. The sharp peaks in the room-temperature emission spectrum are assigned. The number of lines in the region of the ⁵D₀→⁷F₀ transition and the relative intensities of the ⁵D₀→⁷F ₁ and ⁵D₀→⁷F₂ transitions confirm the presence of two local Eu³⁺ environments and strongly distorted Eu³⁺-ligand surroundings. The reasons for the very short emission life time is discussed. The Sm and Tb analogues have also been synthesized.