Non‐centrosymmetric Selenides AZn4In5Se12 (A=Rb, Cs): Synthesis, Characterization and Nonlinear Optical Properties

Two new non‐centrosymmetric polar quaternary selenides, namely, RbZn4In5Se12 and CsZn4In5Se12, have been synthesized and structurally characterized. They exhibit a 3D diamond‐like framework (DLF) consisting of corner‐shared MSe4 (M=Zn/In) tetrahedra, in which the A+ ions are located. Both compounds are thermally stable up to 1300 K and exhibit large transmittance in the infrared region (0.65–25 μm) with measured optical band gaps of 2.06 eV for RbZn4In5Se12 and 2.11 eV for CsZn4In5Se12. Inspiringly, they exhibit a good balance between strong second harmonic generation (SHG) efficiency (3.9 and 3.5×AgGaS2) and high laser‐induced damage thresholds (13.0×AgGaS2). Theoretical calculations based on density functional theory (DFT) methods confirm that such strong SHG responses originate from the 3D DLF structure.