Na7(SeO4)3(IO3) and K2(SeO4)[IO2(OH)]: two new iodate-selenates with short-wave UV cutoff edge and large birefringence

Abstract

Herein, I⁵⁺ with stereochemically active lone pairs (SCALP) was introduced into the selenate system, and two novel iodate-selenates were successfully obtained, Na₇(SeO₄)₃(IO₃) and K₂(SeO₄)[IO₂(OH)]. Innovatively, both the title compounds are potential short-wave ultraviolet (UV) birefringent materials that possess large optical band gaps (4.57 eV and 4.27 eV, respectively) and large birefringence (0.087@546 nm and 0.101@546 nm, respectively). Simultaneously, the powder second harmonic generation (SHG) measurement reveals that Na₇(SeO₄)₃(IO₃) exhibits SHG responses of 0.6 × KDP (KH₂PO₄) with type-I phase matching. Detailed structural analysis and theoretical calculations confirm the excellent optical performance originating from the cooperative effect of [SeO₄] and [IO₃]/[IO₂(OH)] functional units. This work indicates that the iodate-selenate system offers additional candidates for designing short-wave UV optical materials.