Synchrotron-based high-pressure research in materials science Page: 3 of 13
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emission probabilities. The model doesn't predict, for example, the extreme intensity
modulations through resonance.
A very simple case to look at for rare earth emission cross sections are the rare earth
trifluorides such as CeF3. The Ce atom is coplanar with three F atoms, and there is a F above
and below the Ce. All the Ce - F distances are approximately equal. In effect, the Ce atoms are
matrix isolated. Other than dipole forbiddenf-f transitions, this is a large gap insulator.
Figure 1 shows two Energy Distribution Curves (EDCs) of a thin film of CeF3. The small
Fermi step is from the metallic substrate. The 90 eV EDC is below the 4d-4f resonance and the
120 eV EDC is in the main resonance peak. The advantage of CeF3 is that the states of differing
atomic character are well separated so that the relative strength of the emissions can be plotted as
a function of photon energy.
In Figure 2 the relative strengths of the emission features are compared to the calculated
absorption strengths. In all cases, the experimental emission strength is taken as the peak height
since the natural linewidths are significantly greater than the experimental resolution at all
energies. In the case of the Ce 5p, only one spin-orbit split component was used, and even then
the magnitudes of the Ce 5p peaks were scaled down by a factor of three for the plots. Strong
Auger emission in some photon energy ranges prevented reasonable estimates of direct emission
strengths. With all of these provisos, the quantitative agreement over much of the energy range
is surprisingly good. The notable deviation from the absorption cross sections is the increase in
strength of the Ce 5p and loss of strength in the Ce 4f relative to the calculated absorption cross
sections at higher energies. Since the binding energy of the Ce 5p is about 20 eV, the
unpredicted strength of the Ce 5p emission does not cause a problem with the use of calculated
CeF3
120 eV
Ce 5s F 2s Ce 5p F 2p Ce 4f
.90, eV
-60 -40 -20 0
Binding Energy (eV)
absorption cross sections for identifyingf character in the valence band.
Figure 1. Energy Distribution Curves for CeF3 before (90 eV) and at (120 eV) resonance. The
atomic character of each of the peaks is indicated.
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Synchrotron-based high-pressure research in materials science, article, Date Unknown; [Los Alamos, New Mexico]. (https://digital.library.unt.edu/ark:/67531/metadc927438/m1/3/: accessed March 28, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.