Non-π-Conjugated Deep-Ultraviolet Nonlinear Optical Crystal K₂Zn₃(SO₄)(HSO₄)₂F₄

Deep-ultraviolet (deep-UV) (wavelengths of <200 nm) nonlinear optical (NLO) materials are playing an increasingly important role because of their significant technological applications in advanced scientific instruments. In recent years, the non-π-conjugated systems have received extensive attention as new emerging sources of deep-UV NLO materials. Here, a new non-π-conjugated deep-UV NLO material, K₂Zn₃(SO₄)(HSO₄)₂F₄, has been successfully obtained by the hydrothermal method. It has a layered structure formed by [Zn₃(SO₄)(HSO₄)₂F₃]_∞ layers bridged via K-O and K-F bonds. Powder second-harmonic generation shows that K₂Zn₃(SO₄)(HSO₄)₂F₄ can achieve phase matching, and the response is ∼0.3 times that of KH₂PO₄. Remarkably, the single-crystal transmittance spectrum confirms that the absorption edge of K₂Zn₃(SO₄)(HSO₄)₂F₄ is below 200 nm, and the experimentally measured birefringence is 0.0126 at λ = 546 nm. In-depth first-principles calculations illustrate well the microscopic origin of the optical properties. This work enriches the structrual diversity of non-π-conjugated deep-UV NLO materials.