Spectroscopic properties of nonlinear optical LiGaTe2 crystal

Abstract

The nonlinear crystal LiGaTe2 (LGT) with chalcopyrite structure was grown by the Bridgman–Stockbarger technique. LGT is transparent in the 0.52–16μm range. Fundamental absorption edge is due to direct allowed transitions; Band gap values are 2.65 and 2.41eV at 80 and 300K, respectively. Vibrational, Raman and IR absorption spectra demonstrate four groups of lines in the 50–350cm−1. Intense orange photoluminescence (PL) in a broad 605nm band, excited at band-to-band transitions and quenched in the 180–250K range is related to self-trapped excitons. Weaker PL components at 510, 729 and 898nm 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.