Crystal structures and second-order NLO properties of borogermanates

Borogermanates are a class of very important compounds in materials chemistry. In this paper, the syntheses, structures, and properties of metal borogermanates are reviewed. Organically templated borogermanates with zeolite-like open-frameworks show potential applications as microporous materials. Many compounds in alkali or alkaline-earth borogermanate systems are structurally acentric or polar, some of which exhibit excellent Second Harmonic Generation (SHG) coefficients, wide transparency regions, and high optical-damage thresholds as well as excellent thermal stability. Most of the lanthanide borogermanates are structurally centrosymmetric and not SHG active; however, they are able to emit strong luminescence in visible or near-IR region. In the B-rich compounds, BO3 and BO4 groups can be polymerized into a variety of discrete polynuclear anionic cluster units or extended architectures via B–O–B bridges; whereas in the Ge-rich compounds, GeO4 and GeO6 polyhedra can also be polymerized. The combinations of borate and germinate afforded rich structural and topological types.

Graphical abstractBorogermanates are a class of very important compounds in materials chemistry. Both BOx (x=3, 4) and GeOy (y=4, 6) polyhedra can be polymerized into a variety of discrete polynuclear anionic cluster units or extended architectures. The combinations of borate and germanate groups in the same oxide framework not only give rise to a rich structural chemistry, but also afford many polar compounds with good SHG properties.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Borogermanates are a class of new materials. ► They feature to be the combination of B and Ge atoms into the same oxide framework. ► They can form a large number of novel 2D and 3D framework structures. ► Some of them are acentric or polar with moderate strong SHG responses.