Two Lead Halides with Strong SHG Response Obtained by the Isovalent Substitutions of Alkali Metal Cation and Halogen Anion.

The substitution of alkali metal cation or halogen anion based on nonlinear crystals is an effective strategy to exploit new optical materials. The strategy has been successfully expanded to discover two new lead halides, RbPb(CHCOO)X (X = Br, Cl). The substitution of the Cs cation with a Rb cation can not only increase the local dipole moment of the distorted [PbBrO] polyhedron but also reduce the cell unit, resulting in a large net macroscopic polarization. Therefore, RbPb(CHCOO)Br possesses a strong second-harmonic generation (SHG) response (6 × KDP) and a large birefringence (0.18@1064 nm). Furthermore, by the substitution of the Br anion with a Cl anion, RbPb(CHCOO)Cl exhibits a high laser damage threshold (LDT, 84 × AgGaS) and a short UV cutoff edge of 287 nm, as well as moderate SHG response (3 × KDP) and birefringence (0.11@1064 nm). Detailed theory calculations elucidate the origin of the linear and nonlinear optical properties of these compounds.