Optical transitions in ZnSe and CdTe crystals with involvement of the cation $d$ bands

The permittivity spectra $\varepsilon_1(E)$ and $\varepsilon_2(E)$ of ZnSe and CdTe crystals are calculated in the range of 10–25 eV using their experimental reflectance spectra and Kramers–Kronig integral relations. The spectra are decomposed into thirteen and twelve separate transition bands for ZnSe and CdTe, respectively, using the improved nonparametric combined Argand diagram technique. The main spectral parameters, including the maximum energies and halfwidths and oscillator strengths, are determined. The oscillator strengths are found to be within 0.1–1.4 for ZnSe and 0.2–0.7 for CdTe. The obtained $\varepsilon_2(E)$ bands are due to interband and exciton transitions with the involvement of cation core $d$ bands of both crystals under consideration.