K3[TbxEu1–xGe3O8(OH)2] (x = 1, 0.88, 0.67, 0): 2D-Layered Lanthanide Germanates with Tunable Photoluminescent Properties

A family of novel 2D-layered lanthanide germanates K3[TbxEu1–xGe3O8(OH)2] (x = 1, 0.88, 0.67, 0; denoted as TbGeO-JU-87, Tb0.88Eu0.12GeO-JU-87, Tb0.67Eu0.33GeO-JU-87, and EuGeO-JU-87) were synthesized under mild hydrothermal conditions in a concentrated gel system. They are isostructural, as confirmed by the powder X-ray diffraction analysis. The single-crystal X-ray diffraction analysis of EuGeO-JU-87 reveals that it is a 2D-layered [EuGe3O8(OH)2]n3n– anionic framework, which is built up from GeO4H/GeO4 tetrahedra and EuO6 octahedra by sharing vertex O atoms. Charge neutrality is achieved by K+ ions located in the free void space. Interestingly, photoluminescence studies show that Tb0.88Eu0.12GeO-JU-87 and Tb0.67Eu0.33GeO-JU-87 exhibit a high Tb3+-to-Eu3+ energy-transfer efficiency and the TbxEu1–xGeO-JU-87 system displays tunable photoluminescent properties.