Thus, understanding the correlation among the composition, structure, and NLO properties of crystals is still critical in exploring new SHG materials with better performance. As a remarkable source of the NLO material, borates have distinctive advantages, such as the large SHG, excellent UV transmittance, and high damage threshold value, etc.

Prof. Pan Shilie and his team from Xinjiang Technical Institute of Physics and Chemistry, CAS, synthesized a new noncentrosymmetric polyborate, Ba₂[B₆O₉(OH)₄], under a hydrothermal condition. The polyborate contains chiral layers constructed by two kinds of helical chains and also form new B₁₈O₄₂ circles based on B₃O₈ units [(3: Δ+2T)]. One kind of Ba atom locates in the cavity surrounded by the B₁₁O₁₁ ring within the anion layer, and the other kind of Ba atom inserts between two adjacent layers. UV–vis diffuse reflectance spectroscopy demonstrates that the compound has a cutoff edge below 190 nm and has a large second-harmonic generation (SHG) effect, which is approximately 3 times that of KH₂PO₄ (KDP) and is type-I phase matchable.

The result has been published on Inorganic Chemistry , 2012,51(3): 1852-1858. The paper is also archived at http://pubs.acs.org/doi/abs/10.1021/ic2021337.

The work was supported by the Main Direction Program of Knowledge Innovation of Chinese Academy of Sciences, the “National Natural Science Foundation of China”, the “One Hundred Talents Project Foundation Program” of the Chinese Academy of Sciences.

Figure 1. Asymmetric unit of Ba₂[B₆O₉(OH)₄]

Figure 2. (a) Two kinds of spatial connections of the B₃O₈ units: type A and type B. (b) Perspective views of the B₁₁O₁₁ ring and B₁₈O₄₂ circle within the anion layer.