Possible electronic states of gadolinium impurity centers in PbGdS narrow-gap semiconductor: electron paramagnetic resonance data

In the electron paramagnetic resonance spectra of crystals of narrow-gap semiconductor PbGdS (3,2 · 10 ≤ x ≤ 9,5 · 10), unusual changes in the shape of the lines of Gd (4f, S = 7/2) centers were detected, associated with a change in the concentration of impurity gadolinium. In the studied crystals with increased gadolinium concentrations, weaker additional lines of two types of new gadolinium centers with cubic symmetry of magnetic properties and with effective electron spins of S = 7/2 and S = 5/2 were also observed. Two possible explanations for the observed properties of the discovered paramagnetic centers are proposed.