Photoinduced localized magnetic polaron and luminescence in Eu chalcogenides, especially in EuTe

There has been a controversy over the photoexcited electron state in Eu chalcogenides. This paper examines whether the photoexcited electron in Eu chalcogenides, especially in EuTe, is the self-trapped magnetic polaron (STMP) or the photoinduced localized magnetic polaron (PILMP) bound by the 4f hole produced in the photoexcitation process. The theoretical analysis has been performed for the recent systematic spectroscopic study of Eu chalcogenides [J. Phys. Soc. Jpn. 63, 4616 (1994)]. This paper shows that the photoexcited electron in EuTe, associated with the photoluminescence band at 1.47 eV, forms the PILMP state, which brings about the large lattice displacement around the 4f hole through the 4f-hole–optical-phonon interaction, producing a large Stokes shift. The observed value of the Stokes shift is never explained by the STMP model. It is revealed that the attractive Coulomb interaction between the photoexcited electron and the 4f hole is not weak, which supports the magnetic exciton model in the absorption process. The luminescence band at 1.47 eV in EuSe is understood by the same mechanism. The magnetic polaron effect in EuSe is quite large compared with that in EuTe.