Xiaojing Li,Zilong Chen,Fuming Li,Fangfang Zhang,Zhihua Yang,Shilie Pan
A long-lasting challenge in ultraviolet (UV) nonlinear optical (NLO) materials design is to combine conflicting and harsh properties into one structure, including wide UV transparency, strong NLO efficiency, and moderate birefringence to realize phase-matching at short wavelength. A fluorine-directed material design strategy is adopted to accelerate the process of finding NLO materials with optimal performances. In this work, taking LiB 3 O 5 (LBO) as a maternal structure, one O atom with two F atoms is substituted and LiNaB 6 O 9 F 2 which possesses novel double interpenetrating 3 [B 6 O 9 F 2 ] ∞ networks and fluorine-directed optimal performances including enhanced birefringence and phase-matching capacity is successfully obtained. The perfect balance among deep-UV cutoff edge, large second-harmonic generation (SHG) response (1.1 × KDP), and moderate birefringence (0.067 at 1064 nm) of LiNaB 6 O 9 F 2 makes it a promising UV NLO crystal.
Two new isostructural lead borates , Pb 8 Mg(BO 3 ) 6 and Pb 8 Ca(BO 3 ) 6 , have been synthesized via high temperature solution method. The single crystal structures of title compounds contain ∞ [Pb 8 B 6 O 18 ] 2- double layers composed of planar BO 3 triangles, Pb(2)O 9 and distorted Pb(1)O 5 polyhedra, these layers condense in c -axis, and the MgO 6 (or CaO 6 ) polyhedra fill into the layers, forming a three-dimensional framework. The stereochemical activity of lone pair (SCALP) electrons were found in the Pb(1)O 5 polyhedra, which combine with the BO 3 units, generating strong optical anisotropy . The calculated birefringences of Pb 8 Mg(BO 3 ) 6 and Pb 8 Ca(BO 3 ) 6 using first-principles method are 0.15@1064 nm and 0.12@1064 nm, respectively, which are comparable to the commercial α -BaB 2 O 4 (α-BBO) crystal and imply that they probably can be used as birefringent materials. The electronic structures, density of states of title compounds were calculated by density functional theory (DFT). Meanwhile, the TG-DSC curves, infrared spectral and UV–Vis–NIR diffuse reflectance spectral were measured.
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