From Ba[Sn(IO3)6] to Ba[Sn(IO3)4F2]: Fluoride-Ion-Driven Enhancement of Birefringence and Band Gap

Abstract

Birefringent materials have garnered extensive attention as indispensable components in optical devices, including waveplates, polarizers, and optical isolators. In this study, two novel tin iodates birefringence materials, Ba[Sn(IO₃)₆] and Ba[Sn(IO₃)₄F₂], were synthesized via hydrothermal synthesis. It is noteworthy that both materials exhibit outstanding comprehensive properties. The properties of the Ba[Sn(IO₃)₄F₂] material exhibited significant enhancement through the implementation of a fluoride ion partial substitution strategy, in comparison to the properties of the Ba[Sn(IO₃)₆] material. Specifically, the birefringence at 532 nm increased from 0.120 to 0.214, the band gap rose from 3.97 to 4.17 eV, the absorption edge shifted from 272 to 263 nm, and the thermal stability increased from 440 ℃ to 460 ℃. Mechanistic studies indicate that the IO₃⁻ groups are the primary contributors to the phenomenon of birefringence. Concurrently, the presence of fluoride ions has been demonstrated to broaden the band gap and promote the optimized alignment of IO₃⁻ groups. This, in turn, has been shown to achieve simultaneous enhancement of both birefringence and band gap. This work elucidates the mechanism of fluoride ion regulation, providing an effective approach for designing high-performance inorganic birefringent materials.