Electron spin resonance studies of d⁵ ions (Fe³⁺ and Mn²⁺) in lead oxide-lead halide glasses

Abstract

Electron spin resonance (ESR) of d⁵ ions (Fe³⁺ and Mn²⁺) has been investigated in PbO---PbF₂ and PbO---PbCl₂ glasses in wide ranges of composition. ESR spectra of d⁵ ions in these glasses exhibit significant differences which we have attributed to at least three important causes: (i) The ionic potentials of Fe³⁺ and Mn²⁺ are different. Hence Fe³⁺ ions tend to acquire their own environment while Mn²⁺ ions take up substitutional (Pb²⁺ ion) positions. (ii) The sizes and nephelauxetic behaviours of O^2- and F^- ions are similar. Thus even when there is a mixed anionic coordination, the environment of Mn²⁺ ions is highly symmetrical in oxyfluoride glasses. The Mn²⁺ spectra in oxychloride glasses are considerably different. (iii) Increase in halide ion concentration increases the ionicity of lead-ligand bonding and favours a more symmetrical environment around dopant ions in halide-rich glasses. The features in ESR spectra have been interpreted in the light of known behaviour of d⁵ ions in glasses and also in the context of known structural features of PbO---PbX₂ glasses. Dopant ions appear to cluster at high concentrations although isolated low-symmetry sites are still observed. Effects of crystallization and annealing upon ESR spectra have also been investigated.