Energy spectrum of Eu localized states in the PbEuTe solid solution in the middle and far infrared region

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In the project we want to advance the understanding why rare earth ions form localized states in a semiconductor matrix, in particular we are interested in weak interactions that corresponds to the low-energy spectrum of the rare earth ions. The investigations are performed on high-quality epitaxial layers of ionic PbEuTe solid solution. This is a mixture of the PbTe narrow-gap semiconductor and the EuTe wide-gap antiferromagnetic semiconductor, which is of significant practical interest. In optical experiments, localized states are seen as discrete more-or-less narrow lines that indicate the rear-earth interaction with the crystal environment. We want to explain how these lines arise and which interactions determine their spectral properties; in addition, we utilize them to investigate particular properties of solids. Of particular importance are the p-d conduction-bands hybridization, the crystal-field and spin-orbit interactions of both f - and d-electrons, the s-f, p-f and d-f exchange interactions. The magnitude of these interactions has the order of 1 - 200 meV that corresponds to frequencies of 10 - 2x103 cm-1. Hence, we utilize THz and infrared spectroscopy for transmission, reflection and luminescence experiments. In order to avoid the specific phonon absorption region or to shift the Reststrahlen region of the substrates, we grow epitaxial layers on different substrates (BaF2, KCl, Si).