Knowledge Bank

“Absorption bands for certain rare-earth ions in solid state solution have been found in the infrared region in the vicinity of $2000-5000cm-1$. These have been interpreted as electronic transitions arising from crystal field splitting of the ground state. For Ce(III) the absorption ($F\eta 2\leftarrow F5/2$) occurs as a doublet at 2155 and $2250cm-1$, which is apparently quenched by traces of transition metal ions. The splitting varies with the number of interstitial fluoride ions, as shown by addition of NaF and by x-ray density measurements.”