The Eu3+ charge transfer energy and the relation with the band gap of compounds

The location of the energy levels of any of the 13 divalent lanthanides in oxide or fluoride compounds relative to the top of the valence band or the bottom of the conduction band can be obtained by using only three host dependent parameters: (1) the energy of charge transfer from the top of the valence band to Eu3+, (2) the redshift of the first 4f→5d transition in divalent lanthanide ions, (3) the energy of charge transfer from the top of the valence band to the bottom of the conduction band. These three parameters were determined for a large collection of compounds by re-analyzing and retrieving data from literature on optical absorption and luminescence excitation spectra. Data are presented and a first analysis performed. Special attention is given to the systematic behavior in the energy of charge transfer (CT) to Eu3+ with (1) type of anions present in the compound, (2) the strength of binding of valence band electrons, and (3) the size of the site occupied. Also relationships between the CT energy and the band gap energy are explored.