Pressure dependence of 4f levels in europium pentaphosphate up to 400 kbar

The effect of pressure on the fluorescence of Eu3+ ions in Europium pentaphosphate (EuP5O14) was measured up to 400 kbar. We observed a pressure induced "antilevel crossing" of the crystal-field levels within the F17 manifold and a decrease of the spin-orbit and Coulomb interactions for the 4f electrons, which is correlated with an expansion of the 4f-electron wave functions. © 1977 The American Physical Society.