Deep-Ultraviolet Nonlinear-Optical Material K3Sr3Li2Al4B6O20F: Addressing the Structural Instability Problem in KBe2BO3F2

A beryllium-free deep-ultraviolet (DUV) nonlinear-optical (NLO) material, K₃Sr₃Al₄Li₂B₆O₂₀F, has been synthesized and characterized. Unlike KBe₂BO₃F₂ (KBBF), the reported NLO material does not require the use of toxic BeO in the synthesis, and through the judicious selection of cations, strong interlayer interactions are observed that facilitate the crystal growth. K₃Sr₃Al₄Li₂B₆O₂₀F exhibits second-harmonic generation (SHG) at both 1064 and 532 nm with efficiencies of 1.7KH₂PO₄ and 0.3β-BaB₂O₄ and has an absorption edge of 190 nm. Because of the strong interlayer interactions, we were able to grow well-faceted large crystals, 8 × 8 × 5 mm³, through a top-seeded-solution-growth technique. With these crystals, we determined a birefringence of 0.0574 at 1064 nm and a type I phase-matching SHG limit of 224 nm.