One-Dimensional Perovskite RbGeI3 with Large Optical Anisotropy

Inorganic halide perovskites have been regarded as potential candidates for nonlinear optical (NLO) materials due to their large bandgaps and second-harmonic generation (SHG) effects. If these crystals exhibit large optical anisotropy, their birefringent phase-matching ability will undergo enhancement. In this study, a one-dimensional (1D) halide perovskite, RbGeI₃, was experimentally synthesized. Its [GeI₃]_∞¹ double chains are parallelly arranged, resulting in a large structural anisotropy with a birefringence of 0.122@1064 nm, the largest one in reported NLO-active inorganic halide perovskites, as determined from first-principles calculations. Furthermore, a comprehensive characterization involving Raman spectroscopy, the optical absorption spectrum, and powder SHG measurement was conducted to assess its suitability for NLO applications.