Ion-Pair Spectra in Rare Earth Salts

Abstract

An attempt is made to explain the intensities of absorption lines corresponding to the ion-pair transitions which were first observed by Varsanyi and Dieke for the case of Pr ³⁺ ion-pair in PrCl ₃ crystal. An expression for the transition electric dipole moment is derived following Dexter's model under the two assumptions that the levels of the excited configurations of the type (4 f ) ( n ' l ') with odd parity are completely degenerate and the charge distributions of the rare earth ions do not overlap. The relative intensities can be explained fairly well except for a few transitions by introducing an empirical parameter adjusted so as to give a good fit to the observed ones determined by Dieke and Dorman. The values of the parameter are found to be scattered although they should not theoretically. The reason for this discrepancy is discussed.