Spectral-line-broadening study of the trivalent lanthanide-ion series.II. The variation of the electron-phonon coupling strength through the series

The variation of an electron-phonon coupling strength of lanthanide ions is evaluated by measuring the temperature-dependent line broadening of a large number of 4f transitions of nine lanthanide ions. The results show that the electron-phonon coupling strength derived from these line-broadening experiments is large in the beginning (Ce^3+, Pr^3+, Nd^3+) and the end (Er^3+, Tm^3+, Yb^3+) of the trivalent lanthanide-ion series, but small at the center (Eu^3+, Gd^3+, Tb^3+). This trend can qualitatively be explained by the lanthanide contraction and the shielding of the 4f electrons.