Exploring new nonlinear optical (NLO) materials with high laser-induced damage threshold (LIDT) in the infrared (IR) region is vital for the development of technologies relying on tunable laser systems. Herein, we report on a quaternary diamond-like semiconductor, α-Li2ZnGeS4, crystallizing in the polar, noncentrosymmetric orthorhombic space group Pna21. The wide optical bandgap of 4.07 eV prohibits multiphoton absorption, concurrently yielding an impressive LIDT around 61.5× that of the benchmark NLO material AgGaSe2 at 1064 nm. It also features phase-matchability for three-wave mixing. Notably, the large bandgap and the outstanding LIDT of α-Li2ZnGeS4 do not hinder its second harmonic generation (SHG) response. The second-order nonlinear optical coefficient, χ(2), was estimated to be 26 pm/V, which exceeds that of several commercially available IR-NLO crystals. In general, there is usually a trade-off between the LIDT and the NLO coefficient; however, α-Li2ZnGeS4 features an excellent balance between an outstanding LIDT and a strong SHG response, making the compound a promising candidate for next-generation IR-NLO devices.

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Cu2CdSnS4 and α/β-Cu2ZnSiS4 meet several criteria for promising nonlinear optical materials for use in the infrared (IR) region. Both are air-stable, crystallize in noncentrosymmetric space groups, and possess high thermal stabilities. Cu2CdSnS4 and α/β-Cu2ZnSiS4 display wide ranges of optical transparency, 1.4-25 and 0.7-25 μm, respectively, and have relatively large second-order nonlinearity as well as phase matchability for wide regions in the IR. The laser-damage threshold (LDT) for Cu2CdSnS4 is 0.2 GW/cm(2), whereas α/β-Cu2ZnSiS4 has a LDT of 2.0 GW/cm(2) for picosecond near-IR excitation. Both compounds also exhibit efficient third-order nonlinearity. Electronic structure calculations provide insight into the variation in properties.

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The quaternary diamond‐like semiconductor, Cu2ZnSiS4, was synthesized by high‐temperature solid‐state synthesis at 1000 °C. High‐resolution synchrotron X‐ray powder diffraction of this product revealed the presence of two polymorphs. This data confirms that the known α‐Cu2ZnSiS4 exists with the wurtz‐stannite structure in the noncentrosymmetric space group Pmn21. The new polymorph, β‐Cu2ZnSiS4, crystallizes in the noncentrosymmetric space group Pn with a = 6.134092(6) Å, b = 6.392752(5) Å, c = 7.421228(8) Å, β = 90.056(1)°, Z = 2, χ2 = 5.554, Rp = 0.0857 and wRp = 0.1173. Electronic structure calculations performed for both polymorphs indicate direct bandgaps of 1.3 and 1.7 eV at the Γ‐point, respectively.