Dispersion of the refractive index of epitaxial Pb1 − xEuxTe (0 ≤ x ≤ 1) alloy layers below the absorption edge

The transmittance spectra of epitaxial Pb1 − x Eu x Te (0 ≤x ≤ 0.1) alloy layers are exploited to study the dispersion of their refractive index in the spectral range from 650 to 8000 cm−1 (below the absorption edge). The refractive index and the position of the absorption edge as functions of the composition parameter of the alloys are determined at two temperatures, 80 and 295 K. The refractive index is calculated in the context of the classic wave concepts of propagation of electromagnetic radiation. The experimentally determined dispersion dependences are described by the empiric Sellmeier expression of the second order. From analysis of the transmittance of the layers, it follows that the band gap of the epitaxial Pb1 − x Eu x Te alloys increases with increasing temperature at x 0.5.