An advanced experimental and theoretical model to explain the correlation between the electronic and local structure of Eu2+ in two diferent environments within a same compound, EuS, is presented. EuX 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 75d0
?4f 65d1 electronic transition, no consistent model of the pressure-induced modifcations 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 feld plays a major role in
triggering the observed electronic transitions from semiconductor to the half-metal and fnally to the
metallic state.Authors thank the financial support from Projects PGC2018-101464-B-I00, PGC2018-097520-A-I00 and MALTA-Consolider Team RED2018-102612-T (Ministerio de Ciencia, Innovación y Universidades) is acknowledged. V. Monteseguro acknowledges the “Beatriz Galindo” fellowship (BG20/000777) and the “Juan de la Cierva” fellowship (IJC2019-041586-I). Authors are grateful to the staff of the BM23 beamline and the high-pressure laboratory at the ESRF for their support during the experiment (proposal number HC-3913), and the SERCAMAT (SCTI) of the University of Cantabria for FTIR facilities
