Growth, Structure, and Optical Properties of Nonlinear LiGa_0.55In_0.45Te₂ Single Crystals

In search of new nonlinear optical crystals for the mid-IR range, we grew single crystals of LiGa_0.55In_0.45Te₂ (LGITe) of optical quality; its structure was established, and the spectroscopic properties were studied. LGITe crystallizes in a tetragonal chalcopyrite-like (I4̅2d) structure at 667 ± 5 °C. Crystals are transparent in the 0.76–14.8 μm spectral region with some absorption bands related to OH/H₂O and Ge–O vibrations. Analysis of the Tauc plots showed that LGITe is a direct band gap semiconductor with the band gap E_g = 1.837 eV at 300 K. The Raman spectrum for LGITe is very similar to that for LiGaTe₂: the most intense band A₁ near 120 cm^–1 corresponds to the Li–Te vibration. DFT calculations were carried out for the first time to simulate the energy band structure (band gap ∼1.67 eV), density of states (DOS), birefringence (0.049 at 2 μm), and nonlinear susceptibility (d₁₄ = d₃₆ = −48.73 pm/V). For ternary LiInTe₂ these parameters are Δn = 0.007 and d₁₄ = d₃₆ = −61.4 pm/V, respectively. The calculated optical properties indicate that LiGa_0.55In_0.45Te₂ is a promising mid-IR nonlinear optical crystal with nonlinear parameters higher than those of LiGaTe₂.