The birefringence of the new Ba2Na3[B3O6]2F (BNBF) (P63/m) and Ba7(BO3)4−yF2+3y (P63) phases has been investigated. Coefficients of the Sellmeier equations have been determined. Parallel [B3O6]3− rings in the Ba2Na3[B3O6]2F structure generate the major anisotropic polarizabilities and produce large birefringence Δn = 0.1097 − 0.0428 from 350 nm to 5 μm, comparable to that of commercial birefringent crystal α-BaB2O4. A new flux for growing a high quality BNBF crystal has been proposed. In the measured wavelength range from 266 nm to 1.7 μm noncentrosymmetric phase Ba7(BO3)4−yF2+3y (y = 0.49) exhibits low birefringence Δn = 0.0111 − 0.0037 which can be accounted for non-coplanar arrangement of the anionic groups in the structure. Low birefringence prevents the use of this crystal for nonlinear optical applications, since phase-matching conditions for second harmonic generation can not be reached.
|Журнал||Materials Research Bulletin|
|Состояние||Опубликовано - 1 июл 2017|