Coexistence of Strong Second Harmonic Generation Response and Wide Band Gap in AZn4 Ga5 S12 (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 [dij >0.6 × AgGaS2 (AGS)] and wide band gap (Eg >3.5 eV). Herein three new MIR NLO materials, AZn4 Ga5 S12 (A=K, Rb, Cs) are reported, which crystallize in the KCd4 Ga5 S12 -type structure and adopt a 3D diamond-like framework (DLF) consisting of MS4 (M=Zn/Ga) tetrahedra; achieving the desired balance with strong powder SHG response (1.2-1.4 × AGS) and wide band gap (Eg ≈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 AXII4 XIII5 Q12 family, these 3D DLF structures can be used as a highly versatile and tunable platform for designing excellent MIR NLO materials.