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Photoionization and Rydberg spectra of ten lanthanides have been studied using stepwise laser excitation and ionization methods. These spectra Were obtained from several different laser populated excited states in each case. Ac~urate ionization limits were derived from observed photoionization thresholds. Except for praseodymlulll, the observation of one or more long Rydberg progressions allowed more accurate limits to be determined.

The polarized absorption and fluorescence spectra of 0.01–5% Np3+ doped into single-crystal LaCl3 were measured at moderate and high resolution in the range to 50 000 cm−1 at 298, 77, and 4 K. The 150 crystal field components identified were fit by a parametrized model which has previously been shown to provide an excellent account of the energy level structures observed for lanthanides doped into LaCl3. This constitutes the first successful evaluation of the crystal field interaction for an actinide ion in LaCl3 in which J mixing effects were explicitly included. The crystal field parameters for Np3+:LaCl3, B20=163, B40=−632, B60=−1625, and B66=1028, all in cm−1, were determined to be approximately twice as large as those for the analogous lanthanide, Pm3+:LaCl3. From analysis of Zeeman patterns in the fluorescence spectra, the ground state was found to be doubly degenerate, having crystal quantum numbers ±2 and a parallel splitting factor 0.17 LU (Lorentz unit).

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