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.