Coexistence of Strong Second Harmonic Generation Response and Wide Band Gap in AZn Ga S (A=K, Rb, Cs) with 3D Diamond-like Frameworks.

Mid-infrared (MIR, 2-20 μm) second-order nonlinear optical (NLO) materials with outstanding performances are of great importance in laser science and technology. However, the enormous challenge to design and synthesize an excellent MIR NLO material lies in achieving simultaneously a strong second harmonic generation (SHG) response [d >0.6 × AgGaS (AGS)] and wide band gap (E >3.5 eV). Herein three new MIR NLO materials, AZn Ga S (A=K, Rb, Cs) are reported, which crystallize in the KCd Ga S -type structure and adopt a 3D diamond-like framework (DLF) consisting of MS (M=Zn/Ga) tetrahedra; achieving the desired balance with strong powder SHG response (1.2-1.4 × AGS) and wide band gap (E ≈3.65 eV). Moreover, they also show large laser induced damage thresholds (LIDTs, 36 × AGS), a wide range of optical transparency (0.4-25 μm) and ultrahigh thermal stability (up to 1400 K). Upon analyzing the structure-property relationship of AX X Q family, these 3D DLF structures can be used as a highly versatile and tunable platform for designing excellent MIR NLO materials.