Reactions in Crystalline Lattices: Chemistry of Lower Valence States of Lanthanides

Abstract

Reduction of rare-earth (RE) ions to lower valence states in ionic crystals is described in terms of the equilibrium distribution theory for the (alkali halide):RE2+ and (alkaline-earth halide):RE3+ systems. Thermoluminescence glow curves of radiation-reduced CaF2:RE3+ systems reveal that the reoxidation of the divalent ions apparently occurs through thermal excitation of an f electron to the d bands. The additive reduction of RE2+ to the monovalent state in alkali halides yields striking results: While Sm1+ ions in KCl obtained by gamma radiation give rise to broad-band optical spectra which were attributed to 4f66s1 --> 4f56s2 transitions, those obtained through high-temperature additive treatment with liquid K give rise to narrow-line spectra that are not easily interpreted. These results illustrate well the major differences between the radiation reduction and additive reduction processes.