ABSTRACT
Achieving the extreme balance of the key performance requirements is the crucial to breakthrough the application bottleneck for nonlinear optical (NLO) materials. Herein, by assembly of the π-conjugated [B3O6] functional species with the aid of structure-directing property of mer-isomer [YO3F3] octahedra, a new ultraviolet (UV) NLO material, Cs2YB3O6F2 with aligned arrangement of coplanar [B3O6] groups has been synthesized. The polar material exhibits the rare coexistence of the largest second harmonic generation response of 5.6×KDP, the largest birefringence of 0.091 at 532â nm, the shortest Type I phase-matching down to 200.5â nm and deep-ultraviolet transparency among reported acentric rare-earth borates with [B3O6] groups. Remarkably, benefiting from the enhanced bonding force among functional units [B3O6], a firm three-dimensional framework is constructed, which facilitates the growth of large crystals. This can be proved by a block shape crystal with dimensional of 6×5×4â mm3, indicating that it was a promising UV NLO crystal. This work provides a powerful strategy to design UV NLO materials with good performances.
ABSTRACT
Deep-ultraviolet nonlinear optical (DUV NLO) materials are attracting increasing attention because of their structural diversity and complexity. Using the two-dimensional (2D) crystal structure prediction method combined with the first-principles calculations, here we propose layered 18-membered-ring (18MR) boron oxide B2 O3 polymorphs as high-performance NLO materials. 18MR-B2 O3 with the AA and AB stackings are potential DUV NLO materials. The superior performing 18MR-B2 O3 AB has an unprecedentedly high second harmonic generation coefficient of 1.63â pm V-1 , the largest among the DUV NLO materials, three times larger than that of the advanced DUV NLO material KBe2 BO3 F2 and comparable to that of ß-BaB2 O4 . Its unusually large birefringence of 0.196 at 400â nm guarantees the phase-matching wavelength λPM to reach this material's extreme absorption edge of ≈154â nm.