Reflection Spectra of Lanthanides in Thorium (IV) Oxide and the Large Nephelauxetic Effect of Oxide Ligands or Vacancies

Abstract

Retaining the cubic structure, ThO2 can accomodate large concentrations of lanthanides and the equivalent amount of oxygen vacancies. The reflection spectra are measured at 100°K of Nd(III), Sm (III) , Eu (III) , Ho (III) , Er (III) , Tm(III) and Yb(III) in such samples. The excited J-levels correspond to rather broad bands in Thi1-xMjO2-0.5x whereas Nd203 and Er203 have very detailed line groups. The visible spectra indicate a very large nephelauxetic effect in the oxide, the nephelauxetic ratio β being smaller than in the aqua ion to the extent of 0.033 for Nd(III), 0.019 for Sm (III). , 0.017 for Ho (III) , 0.016 for Er (III) and 0.013 for Tm (III) . These values are roughly five times larger than those for the anhydrous chlorides and are quite unexpected.