KB(PO4)F: a novel acentric deep-ultraviolet material

Two challenges to grow KBe2BO3F2 (KBBF), the best known deep-ultraviolet nonlinear optical (NLO) material to date, are the limited crystal sizes and the use of a highly toxic element (Be). Herein we report on the discovery of a novel anhydrous non-centrosymmetric alkali fluorinated borophosphate KB(PO4)F (KBPF) featuring a cut-off wavelength of less than 200 nm and a large second-harmonic generation (SHG) effect similar to KH2PO4 (KDP), hence representing a new promising deep-ultraviolet NLO material. The KBPF crystals consisting of common elements can be grown using green and cost effective processes and do not show any detectable hygroscopicity. The title compound also features a 2-dimensional layer [BPO4F](infinity) built from [BO3F](4-) and [PO4](3-) tetrahedral groups but has much stronger interlayer bonds than KBBF, allowing the growth of large crystals. The title compound has been characterized by PXRD, SEM, TG-DSC, FTIR, UV-Vis-NIR diffuse reflectance and SHG analyses as well as single-crystal X-ray structure refinements. The optical properties of KBPF have also been evaluated by first-principles calculations at the density functional theory (DFT) level.