[M(OH)2]3(IO3)(SeO4)·H2O (M = Ga and In): metal iodate–selenate nonlinear optical materials with a hexagonal tungsten oxide-type topology

Abstract

Exploration of new iodates is crucial due to their splendid applications in the nonlinear optical (NLO) field. Two new IIIA metal iodate–selenates, namely, [M(OH)₂]₃(IO₃)(SeO₄)·H₂O (M = Ga and In), have been successfully synthesized using the hexagonal tungsten oxide (HTO) framework as an ideal structural template. Isostructural [M(OH)₂]₃(IO₃)(SeO₄)·H₂O (M = Ga and In) crystallize in the polar space group P6₃mc. Their structures feature _∞[MO₂(OH)₂]³⁻ (M = Ga, In) layers composed of corner-shared circular M₃O₆(OH)₉ trimeric units based on MO₂(OH)₄ octahedra. The SeO₄ groups are capped above half of the trimeric units of the layers while the IO₃ groups are capped below the remaining trimeric units of the layers. Both compounds exhibit moderate phase-matchable second-harmonic generation (SHG) responses (2.9× and 3.8× KH₂PO₄) under 1064 nm laser radiation and the same band gap of 3.38 eV. Results of theoretical calculations revealed that their SHG effects originated from the synergistic effect of MO₆, IO₃ and SeO₄ groups. So far reports on iodate–selenates are scarce and this work provides a new perspective to design new NLO materials through polar HTO-type topologies and a mixed-anionic strategy.