Outstanding Laser Damage Threshold in Li₂MnGeS₄ and Tunable Optical Nonlinearity in Diamond-Like Semiconductors

The new Li₂MnGeS₄ and Li₂CoSnS₄ compounds result from employing a rational and simple design strategy that guides the discovery of diamond-like semiconductors (DLSs) with wide regions of optical transparency, high laser damage threshold, and efficient second-order optical nonlinearity. Single-crystal X-ray diffraction was used to solve and refine the crystal structures of Li₂MnGeS₄ and Li₂CoSnS₄, which crystallize in the noncentrosymmetric space groups <i>Pna</i>2₁ and <i>Pn</i>, respectively. Synchrotron X-ray powder diffraction (SXRPD) was used to assess the phase purity, and diffuse reflectance UV–vis–NIR spectroscopy was used to estimate the bandgaps of Li₂MnGeS₄ (<i>E</i>_g = 3.069(3) eV) and Li₂CoSnS₄ (<i>E</i>_g = 2.421(3) eV). In comparison with Li₂FeGeS₄, Li₂FeSnS₄, and Li₂CoSnS₄ DLSs, Li₂MnGeS₄ exhibits the widest region of optical transparency (0.60–25 μm) and phase matchability (≥1.6 μm). All four of the DLSs exhibit second-harmonic generation and are compared with the benchmark NLO material, AgGaSe₂. Most remarkably, Li₂MnGeS₄ does not undergo two- or three-photon absorption upon exposure to a fundamental Nd:YAG beam (λ = 1.064 μm) and exhibits a laser damage threshold > 16 GW/cm<sup>2