On the vibronic spectrum of rare earths in calcium fluoride

The phonon side-band peak near 490 cm −1 accompanying 4f → 5d transitions of ten triply-ionized rare earth elements in the CaF 2 matrix and some of the corresponding peaks in SrF 2 and BaF 2 are investigated. All the data taken together confirm an earlier identification of the peaks as a local mode associated with the rare earth ion and its nearest-neighbour fluorine ions.