Optical properties of amorphous Li2O–WO3–B2O3 thin films deposited by electron beam evaporation

Thickness dependencies of the optical properties of as-deposited amorphous 30Li2O–10WO3–60B2O3 thin films prepared by electron beam evaporation on glass substrates at a base pressure of 9 × 10−7 Torr were studied. Glancing angle X-ray diffraction studies were performed to confirm the amorphous nature of the prepared films. The absorption coefficient α (and therefore the extinction coefficient k) was determined from the reflectance and transmission spectra in the strong absorption region. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple–DiDomenico model. The optical constants, such as optical band gap, Urbach energy, the average excitation energy Eo and the dispersion energy Ed, of the thin films were determined. The optical data revealed the existence of allowed indirect transitions.