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.