Optical properties of the γ-phase yttrium trihydride YH3−δ

The transmission spectra of thin films of γ-phase yttrium trihydride YHx, x≅2.87, are measured in the energy range 0.05–6 eV at room temperature. The measured quantities are used to determine the frequency-dependent index of refraction, extinction coefficient, dielectric function, and optical conductivity. In the energy range (E=0.2–6 eV), interband transition and impurity-related transitions dominate the optical properties. In the low-energy range (E=0.05–0.2 eV), hydrogen vibration modes dominate the optical properties. In addition, strong absorption due to free carriers is observed. This work also evaluates several parameters such as plasma frequency, effective carrier density, and donor ionization energy. The possible sources for optical features observed in the spectra are also described.