A nitrate nonlinear optical crystal Pb16(OH)16(NO3)16 with a large second-harmonic generation response

A noncentrosymmetric nitrate, Pb16(OH)16(NO3)16, has been obtained using a hydrothermal method. It is constructed of [Pb4(OH)4](4+) cubanes and nitrate form the overall three-dimensional structure via weak Pb-O bonds. Powder second-harmonic generation (SHG) using the Kurtz-Perry technique shows that Pb16(OH)16(NO3)16 is type I phase-matchable, and the measured SHG coefficient was 3.5 times that of KH2PO4. The direction and magnitude of the dipole moments in PbOn polyhedra and [NO3](-) triangles of Pb16(OH)16(NO3)16 have been quantified using the bond-valence approach, which shows that the large SHG response originates from the cooperation of PbOn polyhedra and [NO3](-) triangles. The band structure and density of states as well as electron density difference are calculated on the basis of density functional theory.