The semiconductors Li(2)CdGeS(4) and Li(2)CdSnS(4), which are of interest for their nonlinear optical properties, were synthesized using high-temperature solid-state and polychalcogenide flux syntheses. Both compounds were found to crystallize in Pmn2(1), with R1 (for all data) = 1.93% and 1.86% for Li(2)CdGeS(4) and Li(2)CdSnS(4), respectively. The structures of both compounds are diamond-like with the tetrahedra pointing in the same direction along the c axis. The alignment of the tetrahedra results in the structure lacking an inversion center, a prerequisite for second-harmonic generation (SHG). A modified Kurtz nonlinear optical powder technique was used to determine the SHG responses of both compounds. Li(2)CdGeS(4) displayed a type I phase-matchable response of approximately 70x alpha-quartz, while Li(2)CdSnS(4) displayed a type I non-phase-matchable response of approximately 100x alpha-quartz. Diffuse-reflectance spectroscopy was used to determine band gaps of 3.10 and 3.26 eV for Li(2)CdGeS(4) and Li(2)CdSnS(4), respectively.

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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 Pna21 and Pn, 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 (Eg = 3.069(3) eV) and Li2CoSnS4 (Eg = 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(2).

Li2SnS3 is a fast Li+ ion conductor that exhibits high thermal stability (mp ∼750 °C) as well as environmental stability under ambient conditions. Polycrystalline Li2SnS3 was synthesized using high-temperature, solid-state synthesis. According to single-crystal X-ray diffraction, Li2SnS3 has a sodium chloride-like structure (space group C2/c), a result supported by synchrotron X-ray powder diffraction and 119Sn Mössbauer spectroscopy. According to impedance spectroscopy, Li2SnS3 exhibits Li+ ion conductivity up to 1.6 × 10–3 S/cm at 100 °C, which is among the highest for ternary chalcogenides. First-principles simulations of Li2SnS3 and the oxide analogue, Li2SnO3, provide insight into the basic properties and mechanisms of the ionic conduction. The high thermal stability, significant lithium ion conductivity, and environmental stability make Li2SnS3 a promising new solid-state electrolyte for lithium ion batteries.

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.