Fano Resonance Investigation of PbTe Layers Containing Eu and Gd Ions

The Fano resonance photoemission studies of Gd/(Pb, Gd)Te layers using synchrotron radiation were carried out and the electronic structure parameters like binding energies of $Gd^{3+}$ 4f and 5p shells, resonance and antiresonance energies for $Gd^{3+}$ were determined. The presence of $Eu^{3+}$ ions was observed in the (Pb, Eu)Te and (Eu, Gd)Te layers grown by MBE technique. The comparison of data for (Pb, Gd)Te compound with corresponding data for (Eu, Gd)Te and (Pb, Eu)Te layers indicates that we are not able to distinct the $Eu^{3+}4f$ and $Gd^{3+}4f$ electrons contribution to the valence band photoemission spectra because of small content od Gd and similar binding energy values. The key parameters allowing to prove exactly the presence of either $Eu^{3+}$ or $Gd^{3+}$ are the resonance and antiresonance energies which are significantly different for these ions and equal to 143 eV/137 eV and 150 eV/142 eV, respectively.