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

Abstract

In search of new nonlinear optical crystals for the mid-IR range, we grew single crystals of LiGa0.55In0.45Te2 (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 (d 14 = d 36 = −48.73 pm/V). For ternary LiInTe2 these parameters are Δn = 0.007 and d 14 = d 36 = −61.4 pm/V, respectively. The calculated optical properties indicate that LiGa0.55In0.45Te2 is a promising mid-IR nonlinear optical crystal with nonlinear parameters higher than those of LiGaTe2.

Ba6In2Ge2Te15: a THz birefringent material with an intriguing quasi-[Te5]4− chain possessing large optical anisotropy and an ultrawide transmission range

“…3b). 28,32,42,43 The reason why the title compound exhibits a wide transmission range is as follows: In general, the frequency of lattice vibrations depends on the atomic mass and the bond length negatively. The heavier the atom and longer the bond length in the crystal, the lower the vibrational frequency will be.…”