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, La 2 B 3 O 4 (OH) 3 (SO 4 ) 2 has been obtained through hydrothermal synthesis , which belongs to polar space group Pna 2(1) (No. 33). Its structure possesses double lanthanum sulfate layers in the ab plane in which the lanthanide ions are bridged by SO 4 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 KH 2 PO 4 . The SHG coefficient of the compound is ascribed to the synergistic effect of SO 4 units and borate units. Meanwhile, distorted LaO x polyhedra also play an important role in the contribution to SHG response.