Investigation on Relationship between Charge Transfer Position and Dielectric Definition of Average Energy Gap in Eu3+-Doped Compounds

The dielectric definition of average energy gap Eg of the chemical bond has been calculated quantitatively in Eu3+-doped 30 lanthanide compounds based on the dielectric theory of chemical bond for complex structure crystals. The relationship between the experimental charge transfer (CT) energy of Eu3+ and the corresponding average energy gap Eg has been studied. The results show that the CT energy increases linearly with increasing of the average energy gap Eg. The linear model is obtained. It allows us to predict the CT position of Eu3+-doped lanthanide compounds with knowledge of the crystal structure and index of refraction. Applied to the Ca4GdO(BO3)3:Eu and Li2Lu5O4(BO3)3:Eu crystals, the predicted results of CT energies are in good agreement with the experimental values, and it can be concluded that the lowest CT energy in Li2Lu5O4(BO3)3:Eu originates from the site of Lu1.