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, Pb3B6O11F2, 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 Pb3B6O11F2 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.