The optical properties of Ag2Te crystals from THz to UV

The optical properties of monoclinic Ag2Te crystals are studied in a wide range (3.7 meV–6.2 eV) of photon energies. The measured reflectivity spectra from THz to UV allow unambiguous a photon energy-dependent complex dielectric function, complex refractive index and absorption coefficient to be obtained. The spectral structure in these optical parameters further indicates the coexistence of an indirect transition with a bandgap energy of about 10 meV and a direct transition with a bandgap energy of about 1.84 eV. •The reflectivity spectra of β-Ag2Te crystals were measured from 3.7 meV to 6.2 eV.•The complex refractive index spectra show n > k at photon energy >33 meV.•An indirect bandgap (∼10 meV) and a direct bandgap (∼1.84 eV) coexist in β-Ag2Te.