La2B3O4(OH)3(SO4)2: A new rare-earth borate-sulfate with second-harmonic generation response

The first example of lanthanide borate-sulfate compound, namely, La2B3O4(OH)3(SO4)2 has been obtained through hydrothermal synthesis, which belongs to polar space group Pna2(1) (No. 33). Its structure possesses double lanthanum sulfate layers in the ab plane in which the lanthanide ions are bridged by SO4 tetrahedra. These layers are further cross-linked by borate chains into the final 3D framework. It is noteworthy that this compound is the first lanthanide borate-sulfate which crystalizes in polar space group and it displays second-harmonic generation (SHG) signal of about 0.1 times that of KH2PO4. The SHG coefficient of the compound is ascribed to the synergistic effect of SO4 units and borate units. Meanwhile, distorted LaOx polyhedra also play an important role in the contribution to SHG response.