Lanthanide threshold limit

The limiting point is often (5). A sensitizer must possess the correct triplet energy in order to sensitize the desired lanthanide ion. It requires then a triplet emission or phosphorescence of the ligand that is higher in energy than a threshold limit fixed by the energy of the lower luminescent excited spectroscopic level of the lanthanide ion. 

Ionization potentials of atoms are usually obtained by the determination of a photoionization threshold or more accurately by the observation of long Rydberg progressions. With the exception of a few of these elements with simple spectra, obtaining such measurements for lanthanides and actinides is difficult if not impossible by conventional spectroscopy. Therefore, very accurate ionization limits were not available for the majority of these elements.( 6)... 

The Rydberg series and photoionization thresholds obtained have permitted the accurate determination of ionization limits for uranium, (1) neptunium, and ten lanthanides. Q)... 

The study of Rydberg spectra and ionization thresholds of ten lanthanides and actinides has been reported by PAISNER et al. [8.80]. In these experiments, high-lying states were accessed by time-resolved stepwise excitation using pulsed dye lasers tuned to resonant transitions. Atoms excited to levels within 1000 cm of the ionization limit were then photoionized by 10.6 ym radiation from a pulsed CO2 laser. The measurements allowed the accurate determination of ionization thresholds from Rydberg convergences to within 0.0005 eV. 

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