Design of Deep-Ultraviolet Zero-Order Waveplate Materials by Rational Assembly of [AlO₂F₄] and [SO₄] Groups

Zero-order waveplates are widely used in the manufacture of laser polarizer waves, which are important in polarimetry and the laser industry. However, there are still challenges in designing deep-ultraviolet (DUV) waveplate materials that satisfy large band gaps and small optical anisotropy simultaneously. Herein, three cases of aluminum sulfate fluorides: Na₂AlSO₄F₃, Li₄NH₄Al­(SO₄)₂F₄, and Li₆K₃Al­(SO₄)₄F₄, with novel [AlSO₄F₃] layers or isolated [AlS₂O₈F₄] trimers were designed and synthesized by the rational assembly of [AlO₂F₄] and [SO₄] groups through a hydrothermal method. Experiments and theoretical calculations imply that these three possess short cutoff edges (λ < 200 nm) and small birefringence (0.0014–0.0076 @ 1064 nm), which fulfils the prerequisite for potential DUV zero-order waveplate materials. This work extends the exploration of DUV zero-order waveplate materials to the aluminum sulfate fluoride systems.