ABi₂(IO₃)₂F₅ (A=K, Rb, and Cs): A Combination of Halide and Oxide Anionic Units To Create a Large Second‐Harmonic Generation Response with a Wide Bandgap

Abstract

A family of nonlinear optical materials that contain the halide, oxide, and oxyhalide polar units simultaneously in a single structure, namely ABi₂ (IO₃ )₂ F₅ (A=K (1), Rb (2), and Cs (3)), have been designed and synthesized. They crystallize in the same polar space group (P2₁ ) with a two-dimensional double-layered framework constructed by [BiF₅ ]^2- and [BiO₂ F₄ ]^5- units connected to each other by four F atoms, in which two [IO₃ ]^- groups are linked to [BiO₂ F₄ ]^5- unit on the same side. A hanging Bi-F bond of [BiF₅ ]^2- unit is located on the other side via ionic interaction with the layer-inserted alkali metal ions to form three-dimensional structure. The well-ordered alignments of these polar units lead to a very strong second-harmonic generation response of 12 (1), 9.5 (2), and 7.5 (3) times larger than that of potassium dihydrogen phosphate under 1064 nm laser radiation. All of them exhibited a wide energy bandgap over 3.75 eV, suggesting that they will have a high laser damage threshold.