Charles Johnson studies glasses and nanoparticles using Mössbauer spectroscopy, most recently using the isotope 151Eu.

The rare earths are an interesting group of elements which form solid compounds with important optical, electrical and magnetic properties which lead to technological applications. They usually form trivalent ions, differing only in the number of electrons n in the 4f shell, ranging from 1 in cerium to 13 in ytterbium. Particularly interesting is europium which can exist in the trivalent (n = 6) as well as the divalent (n = 7) state. Eu2+ is magnetic whereas Eu3+ is non-magnetic, and Eu2+ easily oxidizes to Eu3+. Mössbauer spectroscopy provides a simple method for monitoring the oxidization state, through their different chemical shifts.