Band Gap Energies and Lattice Vibrations of the Lithium Ternary Compounds LiInSe₂, LiInS₂, LiGaSe₂ and LiGaS₂

The band gap energies E G of the lithium compounds have been measured by transmittance and reflectivity measurements as well as measurements of the diffuse reflectivity. At room temperature E G =2.83 eV (LiInSe 2 ), E G =3.56 eV (LiInS 2 ), E G =3.13 eV (LiGaSe 2 ) and E G =3.62 eV (LiGaS 2 ) have been obtained presupposing a direct interband transition. In a first attempt the birefringence of LiInS 2 was studied by transmittance measurements. Using infrared and Raman spectroscopy the lattice vibrational properties have been investigated.