Pb₃B₆O₁₁F₂: The first non-centrosymmetric lead borate fluoride with a large second harmonic generation response

The introduction of Pb²⁺ cations with the lone pair effect and the largest electronegativity of F^- anions successfully results in a new non-centrosymmetric lead borate fluoride, Pb₃B₆O ₁₁F₂, which possesses a large SHG response about four times that of KH₂PO₄ (KDP) and is type-I phase matchable. The structure is built from a 3-dimensional B-O network composed of hexaborate B₆O₁₄ groups and novel [FPb₃]_∞ layers. First-principles electronic structure calculations show that the calculated birefringence of Pb₃B₆O₁₁F ₂ is about 0.07 in the visible region. Based on the measurement of the UV-Vis-NIR diffuse-reflectance spectrum, it exhibits a wide transparency range with a short UV cut-off edge at about 240 nm. All these properties indicate that Pb₃B₆O₁₁F₂ is a promising nonlinear optical crystal in the UV region.