Nonlinear optical (NLO) crystals are the key component in solid-state lasers. New second-harmonic generation (SHG) effective halides, Cs 3 Pb 2 (CH 3 COO) 2 X 5 (X = I, Br), have been rationally synthesized by introducing acetate groups into lead halide perovskites under moderate solvothermal conditions. Cs 3 Pb 2 (CH 3 COO) 2 X 5 (X = I, Br) feature highly oriented anionic chains constructed by distorted [PbX 4 O 2 ] (X = I, Br) polyhedrons. Both the theoretical studies and the dipole moment calculations uncover that their SHG effects are mainly originated from the distorted [PbX 4 O 2 ] (X = I, Br) polyhedrons. Remarkably, Cs 3 Pb 2 (CH 3 COO) 2 I 5 exhibits strong phase-matching SHG response (8 KDP) and large birefringence (0.26@ 1064 nm). Moreover, Cs 3 Pb 2-(CH 3 COO) 2 X 5 (X = I, Br) also possess high laser damage threshold (LDT) which are almost 27 and 41 times that of AgGaS 2 , respectively.

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, Rb 3 Pb 2 (CH 3 COO) 2 X 5 (X = Br, Cl). The substitution of the Cs + cation with a Rb + cation can not only increase the local dipole moment of the distorted [PbBr 4 O 2 ] polyhedron but also reduce the cell unit, resulting in a large net macroscopic polarization. Therefore, Rb 3 Pb 2 (CH 3 COO) 2 Br 5 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, Rb 3 Pb 2 (CH 3 COO) 2 Cl 5 exhibits a high laser damage threshold (LDT, 84 × AgGaS 2 ) 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.