Linear optical susceptibilities of the oxoborate (Pb3O)(2)(BO3)(2)WO4: theory and experiment

The optical susceptibilities have been investigated experimentally and theoretically for a newly synthesized oxoborate, (Pb3O)(2)(BO3)(2)WO4. The crystal structure is composed of one-dimensional chains formed by corner-sharing OPb4 tetrahedra. BO3 and WO4 groups are located around the chains to hold them together via Pb-O bonds. The solid-state fluorescence spectrum exhibited a maximum emission peak at around 375.2 nm with excitation light of 280 nm. UV-Vis diffuse reflectance spectra showed a band gap of about 2.9 eV which compares well with our theoretical band gap of about 2.3 eV obtained using the local density approximation and 2.6 eV using the Engel-Vosko's generalized gradient approximation. We have optimized the atomic positions starting from our X-ray diffraction data so as to minimize the forces on each atom. A remarkable finding is that this crystal possesses a weak anisotropy among three components of the frequency-dependent dielectric function and a small positive birefringence. This indicates that the oxoborate, (Pb3O)(2)(BO3)(2)WO4, cannot be used to produce second harmonic generation (SHG) and optical parametric oscillation