  We analyze the influence of unconventional superconductivity on crystalline
electric field (CEF) excitations of rare earth ions in novel superconductors.
We show that resonant magnetic excitations of the conduction electrons that
have been observed in these systems below T$_c$ may result in the formation of
the bound state in the 4$f$-electron susceptibility. This occurs at energies
well below the CEF excitation energy. The effect is discussed as a function of
temperature and the strength of the coupling between the 4$f$ and
$d$-electrons. We argue that these effects may be present in the layered
cuprates and ferropnictides which contain rare-earth ions.
