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

A family of nonlinear optical materials that contain the halide, oxide, and oxyhalide polar units simultaneously in a single structure, namely ABi2(IO3)2F5 (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 [BiO2F4]5− units connected to each other by four F atoms, in which two [IO3]− groups are linked to [BiO2F4]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. Harmonic generator: A combination of polar halide and oxide anionic groups creates a family of promising mid‐IR nonlinear optical crystals, ABi2(IO3)2F5 (A=K, Rb, and Cs). They have a strong second‐harmonic generation response of 12 (K), 9.5 (Rb), and 7.5 (Cs) times larger than that of potassium dihydrogen phosphate and a wide energy bandgap of over 3.75 eV.