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

AbstractDiscovery of new efficient nonlinear optical (NLO) materials with large second‐order nonlinearity for the short‐wave ultraviolet spectral region (λPM≤266 nm, PM=phase‐matching) is still very challenging. Herein, a new beryllium‐free borate CaZn2(BO3)2 with Sr2Be2B2O7 (SBBO) double‐layered like configuration was rationally designed, which not only preserves the structural merits but also eliminates the limitations of the SBBO crystal. CaZn2(BO3)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[Zn2O6]∞ polar chains with a large net dipole moment and [BO3] units with a high NLO active density. Our findings show the great significance of the [ZnO4] 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.