PbTeVO: A Lead Vanadate Tellurate with Wide Mid-IR Transparency and Large Birefringence Induced by Multiple Birefringence-Active Groups.

Birefringent materials as the key materials in laser science and technology have attracted continuous attention due to their ability to modulate polarized light. Herein, a new lead vanadate tellurate, PbTeVO, has been synthesized through the rational integration of different kinds of birefringence-active functional units. PbTeVO features a unique two-dimensional (2D) [TeVO] layered structure consisting of [VO] and [TeO] octahedra, and Pb cations reside between the [TeVO] layers. In addition, the rare edge-sharing mode of [VO] and [TeO] octahedra was found in this structure. Attributed to the high polarizability and appropriate arrangement of PbO, VO, and TeO units, PbTeVO possesses a great theoretical birefringence of 0.275 at 532 nm, which is the largest among the vanadate tellurate family. The spectral tests also prove that PbTeVO showcases a broad transparency window (439 nm-10 μm), covering an important mid-infrared (IR) atmospheric window (3-5 μm). In addition, in order to improve the transparency, alkali and alkaline earth metal cations were introduced by the substitution strategy, and then the compound KSrTeO was synthesized. It owns a shorter ultraviolet (UV) cutoff edge of 234 nm and a wider transparency window (234 nm-13.8 μm). The findings of PbTeVO and KSrTeO enrich the structure chemistry of the tellurate family and provide new insights for designing new compounds with large optical anisotropy and wide spectral transparency.