Crystal-field mediated electronic transitions of EuS up to 35 GPa

n advanced experimental and theoretical model to explain the correlation between the electronic and local structure of Eu ^2+ in two different environments within a same compound, EuS, is presented. Eu X monochalcogenides ( X : O, S, Se, Te) exhibit anomalies in all their properties around 14 GPa with a semiconductor to metal transition. Although it is known that these changes are related to the 4f^7 5d^0 → 4f^6 5d^1 electronic transition, no consistent model of the pressure-induced modifications of the electronic structure currently exists. We show, by optical and x-ray absorption spectroscopy, and by ab initio calculations up to 35 GPa, that the pressure evolution of the crystal field plays a major role in triggering the observed electronic transitions from semiconductor to the half-metal and finally to the metallic state.