Regulating KBBF-like structures via a charge-assisted hydrogen-bonded framework to enable easily grown ultraviolet nonlinear optical crystals

Abstract

Growing large, high-quality nonlinear optical (NLO) crystals remains a central challenge for advancing ultraviolet (UV) laser technologies. KBe₂BO₃F₂ (KBBF)-type crystals exhibit outstanding NLO properties but suffer from pronounced layer separation that impedes the growth of application-scale single crystals. Here, we introduce a three-dimensional (3D) charge-assisted hydrogen-bonded framework strategy by incorporating sulfanilamide and nitrate anions as hydrogen-bond donors and acceptors into a KBBF-like structure. This approach led to the successful synthesis of a novel ultraviolet (UV) NLO crystal, C₆H₉N₂SO₂·NO₃ (SAN), which preserves a KBBF-like architecture while being stabilized by an extensive hydrogen-bonding network. SAN demonstrates a stronger second-harmonic generation (SHG) response (2.5 × KH₂PO₄, KDP) and higher birefringence (0.112 at 546 nm) compared with KBBF. Crucially, the 3D hydrogen-bonded network suppresses layer exfoliation and enables direct growth of centimeter-scale crystals (4.5 × 1 × 0.5 cm³) from aqueous solution by simple evaporation at room temperature. This work pioneers the integration of hydrogen-bonded framework design into the structural modification of NLO crystals. Through rational hydrogen-bond engineering within the KBBF-type framework, the crystal growth behavior has been significantly improved, establishing a generalizable strategy for modifying other layered functional crystalline materials.