Cs2GeB4O9: a New Second-Order Nonlinear-Optical Crystal

• Published in: Inorganic chemistry Vol. 52; no. 10; pp. 5831 - 5837
• Main Authors: Xu, Xiang, Hu, Chun-Li, Kong, Fang, Zhang, Jian-Han, Mao, Jiang-Gao, Sun, Junliang
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 20.05.2013
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic302774h

A new alkali-metal borogermanate with noncentrosymmetric structure, namely, Cs2GeB4O9, has been discovered, and a large crystal with dimensions of 20 × 16 × 8 mm3 has been grown by a high-temperature top-seeded solution method using Cs2O–B2O3 as a flux. The compound crystallizes in the tetragonal space group I4̅ with a = b = 6.8063(2) Å, c = 9.9523(7) Å, V = 461.05(4) Å3, and Z = 2. It features a three-dimensional anionic open framework based on GeO4 tetrahedra and B4O9 clusters that are interconnected via corner-sharing, forming one-dimensional channels of nine-/ten-membered rings along the a and b axes, which are occupied by Cs+ cations. Cs2GeB4O9 exhibits a very high thermal stability with a melting point of 849 °C, and it possesses a short-wavelength absorption edge onset at 198 nm determined by UV–vis transmission spectroscopy measurements on a slab of polished crystal. Powder second-harmonic generation (SHG) measurement on sieved crystals reveals that Cs2GeB4O9 is a type I phase-matchable material with a strong SHG response of about 2.8 × KH2PO4. The preliminary investigation indicates that Cs2GeB4O9 is a new promising second-order nonlinear-optical crystalline material.