Electron spin resonance studies of d 5 ions (Fe 3+ and Mn 2+) in lead oxide—lead halide glasses

Abstract

Electron spin resonance (ESR) of d 5 ions (Fe 3+ and Mn 2+) has been investigated in PbOPbF 2 and PbOPbCl 2 glasses in wide ranges of composition. ESR spectra of d 5 ions in these glasses exhibit significant differences which we have attributed to at least three important causes: (i) The ionic potentials of Fe 3+ and Mn 2+ are different. Hence Fe 3+ ions tend to acquire their own environment while Mn 2+ ions take up substitutional (Pb 2+ 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 Mn 2+ ions is highly symmetrical in oxyfluoride glasses. The Mn 2+ 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 d 5 ions in glasses and also in the context of known structural features of PbOPbX 2 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.