Spectral Intensities of the Trivalent Lanthanides and Actinides in Solution. I. Pr3+, Nd3+, Er3+, Tm3+, and Yb3+

We have correlated the experimentally measured intensities of the solution absorption spectra of Pr³⁺, Nd³⁺, Er³⁺, Tm³⁺, and Yb³⁺ in three different solvents with a theoretical expression derived by Judd. The expression, $$\begin{array}{c}\mathrm{P=}\mathbf{\Sigma }{\displaystyle {lim}_{\lambda }}{T}_{\lambda }{\mathrm{\sigma (f}}^N{\psi }_J\Vert {\mathbf{\cup }}^{\mathrm{(\lambda )}}{\mathrm{\Vert f}}^N{\psi }_{J^{\prime }}^{\prime }{)}^2\\ \text{λ=2,4,6}\end{array}$$ is derived from a theory in which the ligand‐field interactions with the central 3+ ion cause a mixing of higher configurations of opposite parity into the f^N configuration and gives rise to induced electric‐dipole transitions. A prerequisite for the intensity calculations is the computation of complete intermediate coupling eigenvectors for the energy levels investigated. Other possible mechanisms such as magnetic‐dipole and electric‐quadrupole transitions are considered. The oscillator strengths of important magnetic‐dipole transitions are tabulated. The results give the first experimental verification of the ability of the theory to account for large changes in certain bands of the same lanthanide observed in different solvents. Conclusions are drawn respecting the T_λ's obtained in a given medium for all the lanthanides studied, and also for those obtained for a given lanthanide in different media. The J dependence of the T_λ's is removed to facilitate their intercomparison, and the resulting parameters are tabulated. The T_λ's for Yb³⁺ are obtained by an extrapolation of the values computed for Tm³⁺ and Er³⁺. The nature of the model required by the theory is discussed.