Mossbauer spectroscopy valence fluctuation

At the present time the electron-spectroscopic manifestations of 4f-hybridization in heavy lanthanide materials are scarce. (The so-called valence fluctuating compounds containing the elements Sm, Eu, Tm or Yb are discarded here (see section 7.3).) Nevertheless, indications for a coupling of the f states with band states have been found in materials where the Eu atoms, according to Mossbauer spectroscopy and the magnetic susceptibility, are in the divalent 4f configuration. The XPS 3d core level spectra of a few systems, like Eu metal, EuAlj, EuCuj, EuAgj (Schneider... 

In summary, the two pronounced deviations from standard f electron structure, i.e., valence fluctuations and f band formation can both be studied well by Mossbauer spectroscopy. High-pressure studies are of profound importance in this context. 

---