ABi 2 (IO 3 ) 2 F 5 (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 ABi 2 (IO 3 ) 2 F 5 (A=K ( 1 ), Rb ( 2 ), and Cs ( 3 )), have been designed and synthesized. They crystallize in the same polar space group ( P 2 1 ) with a two‐dimensional double‐layered framework constructed by [BiF 5 ] 2− and [BiO 2 F 4 ] 5− units connected to each other by four F atoms, in which two [IO 3 ] − groups are linked to [BiO 2 F 4 ] 5− unit on the same side. A hanging Bi−F bond of [BiF 5 ] 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.