A Lanthanum Ammonium Sulfate Double Salt with a Strong SHG Response and Wide Deep‐UV Transparency

Abstract The targeted synthesis of deep‐ultraviolet (deep‐UV) nonlinear optical (NLO) materials, especially those with non‐π‐conjugated sulfates, has experienced considerable difficulties due to the need to reconcile the oft‐competing requirements for deep‐UV transparency and strong second‐harmonic generation (SHG). We report herein the designed synthesis of the first rare‐earth metal‐based deep‐UV sulfate La(NH 4 )(SO 4 ) 2 by a double‐salt strategy involving introduction of complementary cations, together with optical studies that reveal a short‐wavelength deep‐UV absorption edge (below 190 nm) and the strongest SHG response among deep‐UV NLO sulfates (2.4×KDP). Theoretical calculations and crystal structure analysis suggest that the excellent balance between SHG response and deep‐UV transparency can be attributed to a synergistic interaction of the hetero‐cations La 3+ and NH 4 + , which optimize alignment of the SO 4 tetrahedra and highly polarizable LaO 8 polyhedra.