P. R. Fields

Electronic Energy Levels in the Trivalent Lanthanide Aquo Ions. I. Pr3+, Nd3+, Pm3+, Sm3+, Dy3+, Ho3+, Er3+, and Tm3+

The free‐ion energy‐level schemes of the Pr3+, Nd3+, Pm3+, Sm3+, Dy3+, Ho3+, Er3+, and Tm3+ aquo ions have been determined from their absorption spectra in dilute acid solution at 25°. Energy‐level assignments were made by comparison with crystal spectra, and on the basis of correlations between calculated and observed band intensities. For most of the ions, it was possible to identify several transitions giving rise to bands at energies as high as 45 000–50 000 cm−1. Sufficient numbers of assignments were made to justify inclusion of the effects of configuration interaction in the calculation of the energy‐level parameters. Variation of the electrostatic, spin–orbit coupling, and configuration‐interaction parameters across the lanthanide series is examined.

Spectral Intensities of the Trivalent Lanthanides and Actinides in Solution. II. Pm3+, Sm3+, Eu3+, Gd3+, Tb3+, Dy3+, and Ho3+

We have correlated the experimentally determined band intensities in the solution absorption spectra of the trivalent lanthanides with a theoretical expression derived by Judd. The spectra were measured in a single medium, dilute acid solution, and, in most cases, in the range ≈6000–50 000 cm−1. In general, the correlation between calculated and observed intensities was very good, even at higher energies. The variation of the intensity parameters over the series is discussed as is the somewhat unexpected degree of correlation obtained in the ultraviolet region.

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, P=Σ lim λTλσ(fNψJ‖∪(λ)‖fNψJ′′)2λ=2,4,6 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 fN 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 dra...

Electronic Energy Levels of the Trivalent Lanthanide Aquo Ions. III. Tb3

The free‐ion energy level scheme of Gd3+ (aquo) to ∼52 000 cm−1 has been determined from the absorption spectrum of Gd3+ in dilute acid solution at 25°C. Several new absorption bands near 50 000 cm−1 have been ascribed to transitions from the ground state to components of the 6G multiplet. Energy level assignments were made on the basis of correlations between calculated and observed intensities. The resulting parameters were: E1 = 5761, E2 = 28.02, E3 = 582.0, ζ4f = 1450, α = 22.55, β = − 103.7, γ = 997.

1S0 Level of Pr3+ in Crystal Matrices and Energy‐Level Parameters for the 4f2 Configuration of Pr3+ in LaF3

The absorption spectrum of Pr3+ in LaF3, LaCl3, CaF2, Pr(Y)Cl3·6H2O, and Pr2(SO4)3·8H2O was investigated. Evidence for the 1S0 level in Pr3+:LaF3 at 46 986 cm−1 is presented; this level was not observed directly in absorption in any of the other matrices studied. An analysis of the 13 observed levels in Pr3+:LaF3, based in part upon a re‐examination of the experimentally observed crystal‐field components of certain levels, gave the following electrostatic, spin–orbit, and configuration‐interaction parameters: E1 = 4559.0, E2 = 21.954, E3 = 467.75, ζ4f = 744.44, α = 15.294, β = − 669.02, γ = 1411.8, with an rms deviation= 33 cm−1.

Low‐Temperature Optical Absorption of Americium Halides

Absorption spectra at low temperatures are reported for AmCl3, AmBr3, and AmI3. Bathochromic shifts have been generally observed in the series from the chloride to the iodide. These shifts are comparable to those observed in lanthanide halides. Hypersensitive transitions have been observed in AmI3. A number of new assignments of excited levels of Am(III) are proposed on the basis of intensity calculations. Electrostatic, spin–orbit, and configuration‐interaction parameters were obtained by direct diagonalization and least‐squares fitting to 29 observed levels for AmCl3. The parameter values in cm−1 are: E1 = 3582.8, E2 = 17.276, E3 = 334.30, ξ5f = 2593.3, α = 21.634, β = − 158.48, γ = 1240.4.

Optical Absorption Spectra of Er3+:LaF3 and ErCl3 · 6H2O

The absorption spectra of Er3+:LaF3 and ErCl3 · 6H2O were investigated in the visible and ultraviolet regions at 4°K. Transitions to practically all of the J levels occurring at <50 000 cm−1 have now been observed. Theoretical analysis of the results including the effects of configuration interaction as expressed in both two‐ and three‐body operators made possible a good correlation between calculated and observed free‐ion level energies. Comparison of the levels observed in the crystal matrices with reported gaseous free‐ion levels suggested some inconsistencies in the latter, but indicated that there is little change in the J‐level structure in the 4f11 configuration when Er3+ is incorporated in the crystal lattices studied.

Absorption Spectrum of Tm3+:LaF3

The absorption spectrum of Tm3+:LaF3 was measured in the region 0.2–2.0 μ which encompasses all but one of the excited states in the 4f12 configuration. Centers of gravity of the observed crystal‐field components of each level were computed and used as the basis for determining the free ion energy level parameters. In addition to the electrostatic and spin–orbit interactions, the effects of configuration interaction and certain two‐body magnetic interactions were considered. The theoretical analysis of the results yielded an excellent agreement between calculated and observed free ion levels.

Optical Absorption Spectra of Gd3+:LaF3 and GdCl3·6H2O

The absorption spectra of single crystals of Gd3+:LaF3 and GdCl3·6H2O were examined at low temperatures and high resolution. Stark components belonging to the 6G multiplet near 50 000 cm−1 were observed in both matrices. Theoretical treatment of the data confirmed the importance of including two‐body magnetic interactions in the analysis.

Absorption Spectrum of PuCl3

The absorption spectrum of thin films of PuCl3 was measured at 298, 77, and 4°K in the range 6000–34 000 cm−1. Results were compared to earlier work in LaCl3 :Pu3+, and a number of new assignments were made. Electrostatic, spin–orbit, and configuration‐interaction parameters were obtained by direct diagonalization of the energy matrix and a least‐squares fitting process to 30 observed levels. The variations in certain energy‐level parameters within the actinide series is discussed. Intensity calculations gave only moderate agreement with oscillator strengths of observed bands.