Layered perovskite-like nitrates A2Ca(NO3)2Cl2 (A = Rb, Cs) as ultraviolet birefringent optical materials

The progress of all-inorganic Ruddlesden–Popper (RP) perovskites broadens the selection of materials suitable for optoelectronic applications, especially in improving stability and performance. Two new alkali metal calcium halide nitrate-based layered RP perovskite variants, Rb2Ca(NO3)2Cl2 and Cs2Ca(NO3)2Cl2, have been synthesized through a facile solution evaporation method. Remarkably, the title compounds exhibit a unique RP perovskite-like nitrate layered structure with significant birefringence (0.099–0.104@546 nm) and short ultraviolet (UV) absorption wavelengths (220–225 nm). In-depth structural investigation and theoretical analyses indicate that the birefringence substantially arises from the planar triangular [NO3] groups. This study not only enhances the structural diversity of layered perovskites but also provides an effective strategy for the continued investigation of all-inorganic birefringent optical materials in the UV region.