Spectroscopic properties of nonlinear optical LiGaTe2 crystal

• LiGaTe2 crystals of optical quality were grown by Bridgman–Stockbarger technique.
• Band gap is 2.65 eV at 80 K and decreases linearly with temperature: dEg/dT = 1.106 × 10−3 eV/K.
• Intense orange luminescence at T < 250 K is due to recombination of self-trapped excitons.
• Valence band is split into 3 components by crystal field and spin–orbit interaction.

The nonlinear crystal LiGaTe2 (LGT) with chalcopyrite structure was grown by the Bridgman–Stockbarger technique. LGT is transparent in the 0.52–16 μm range. Fundamental absorption edge is due to direct allowed transitions; Band gap values are 2.65 and 2.41 eV at 80 and 300 K, respectively. Vibrational, Raman and IR absorption spectra demonstrate four groups of lines in the 50–350 cm−1. Intense orange photoluminescence (PL) in a broad 605 nm band, excited at band-to-band transitions and quenched in the 180–250 K range is related to self-trapped excitons. Weaker PL components at 510, 729 and 898 nm are associated supposedly with F-centers and their complexes. According to PL excitation spectra valence band is split into three components: Γ7(A), Γ6(B) and Γ7(C), from which electrons are excited to the bottom of the conduction band Γ6. The crystal field splitting (ΔCF) and the spin–orbit splitting (ΔSO) were determined to be −0.75, and 0.62 respectively, at liquid nitrogen temperature.