Cs₃B₃O₃F₆ with a Deep-Ultraviolet Cutoff Edge and a Suitable Birefringence as the Potential Zero-Order Waveplate Material

The zero-order waveplates, the essential materials in altering the polarization state of optical waves, are significant in polarimetry and the laser industry. Restricted by birefringence and absorption edge, few materials can have moderately small birefringence (Δ<i>n</i> < 0.01) and a deep-ultraviolet (DUV; λ < 200 nm) transparency range. We used the B₃O₃F₆ unit for designing the zero-order waveplate material, which is composed of three BO₂F₂ tetrahedra interconnected by corner sharing. Here we obtained a new Cs₃B₃O₃F₆ compound with the isolated B₃O₃F₆ unit by a high-temperature solution method, which has the DUV cutoff edge and suitable birefringence (0.0069 at 532 nm) based on the experimental and computational results. This demonstrates that the isolated B₃O₃F₆ unit is a potential group, which favors the search for suitable compounds for DUV zero-order waveplate materials.