ABi2(IO3)2F5 (A = K, Rb, and Cs): ACombination 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)(IO3)(2)F-5 (A=K (1), Rb (2), and Cs (3)), have been designed and synthesized. They crystallize in the same polar space group (P2(1)) 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.