Strong Nonlinearity Induced by Coaxial Alignment of Polar Chain and Dense [BO3] Units in CaZn2(BO3)2

Abstract Discovery of new efficient nonlinear optical (NLO) materials with large second‐order nonlinearity for the short‐wave ultraviolet spectral region ( λ P M ≤266 nm, PM=phase‐matching) is still very challenging. Herein, a new beryllium‐free borate CaZn 2 (BO 3 ) 2 with Sr 2 Be 2 B 2 O 7 (SBBO) double‐layered like configuration was rationally designed, which not only preserves the structural merits but also eliminates the limitations of the SBBO crystal. CaZn 2 (BO 3 ) 2 shows a large PM second harmonic generation (SHG) reponse of 3.8×KDP, which is 38 times higher than that of its barium analogue. This enhancement mainly originates from the 1 [Zn 2 O 6 ] ∞ polar chains with a large net dipole moment and [BO 3 ] units with a high NLO active density. Our findings show the great significance of the [ZnO 4 ] tetrahedra introduced strategy to design beryllium‐free SBBO‐type NLO crystals and also verify the feasibility of using simple non‐isomorphic substitution to induce giant second‐order nonlinearity enhancement.