Cs2CdV2O6Cl2 and Cs3CdV4O12Br: two new non-centrosymmetric oxyhalides containing d(0) and d(10) cations and exhibiting second harmonic generation activity

摘要

Two new oxyhalides including d(0) and d(10) cations, Cs4Cd2V4O12Cl4 (1) and Cs3CdV4O12Br (2), were successfully synthesized via a solid phase reaction. Their crystal structures have been determined by X-ray single crystal diffraction. Compound 1 crystallizes in space group Cm (no. 8), whereas compound 2 is found in space group Cmm2 (no. 35). The corner-shared V3O8 units and CdO2Cl4 units in the compound 1 bridge a three-dimensional network, whereas the corner-shared V4O11 polyhedron and CdO4Br2 octahedron in the compound 2 form a three-dimensional structure. All the polar groups align in one direction, which results in a favorable net polarization. Powder second harmonic generation, using 1064 nm incident radiation, indicates that they are phase-matchable with observable and strong SHG response (5 and 7 times KH2PO4, respectively). The UV-vis-NIR diffuse reflectance spectra indicate that the band gaps of the compound 1 and 2 are 3.00 eV (413 nm) and 3.13 eV (396 nm), respectively. Based on the IR and UV-vis-NIR data, the transparent range of both compounds is 0.4-10.4 mu m. Furthermore, the electronic structure was also investigated by the first-principles calculations.