Lead Mixed Oxyhalides Satisfying All Fundamental Requirements for High-Performance Mid-Infrared Nonlinear Optical Materials.

To design high-performance mid-infrared (mid-IR) nonlinear optical (NLO) materials, we have focused on the combination of a heavy metal lone pair cation, Pb2+ and mixed oxyhalides. A systematic investigation in PbO-PbCl2 -PbBr2 system led us to discover the first examples of NLO lead mixed oxyhalides, namely, Pb13 O6 Cl4 Br10 , Pb13 O6 Cl7 Br7 , and Pb13 O6 Cl9 Br5 . All the reported materials have remarkably comprehensive properties including broad IR transparency (up to 14.0 μm), qualified second harmonic generation (SHG) responses (0.6-0.9×AgGaS2 ), wide band gaps (3.05-3.21 eV), and ease of crystal growth. Interestingly, a centimeter-sized single crystal (2.9×1.3×0.5 cm3 ) of Pb13 O6 Cl9 Br5 revealing a wide transparent range (0.384-14.0 μm) and high laser damage threshold (LDT) (14.6×AgGaS2 ) has been successfully grown in an open system. The study suggests that all the reported mixed oxyhalides are outstanding candidates for mid-IR NLO materials.