High Eu 4f low-energy oscillator strength in the isostructural rare-earth Zintl compounds EuIn ₂X ₂ (X=P,As)

The isostructral Zintl compounds EuIn ₂X ₂ (X=P,As) are investigated within density functional theory. We employ the local spin density approximation with onsite interaction (LSDA+U) for varying U from 0 eV to 7 eV to model the Coulomb repulsion of the Eu 4f electrons. The LSDA+U optical conductivity disagrees with the experimental spectrum, while the simple LSDA is successful. Contrary to the expectation, it is found that EuIn ₂X ₂ (X=P,As) has a large oscillator strength for the f → d transitions in the low-energy range (below 1.5 eV) in which effects of the joint density of states play a key role. The materials show a sizeable magneto-optical Kerr effect.