Electron spin resonance spectra of Eu 2+ and Tb 4+ ions in glasses

Electron spin resonance (ESR) spectra of Eu 2+ and Tb 4+ were observed at room temperature in one fluoride phosphate and two phosphate glasses. Although both ions are isoelectronic, they have different ESR spectra. Eu 2+ ions exhibit pronounced features at effective g-values of 2.0, 2.8 and 6.0, which is typical for the so-called U-spectrum. Tb 4+ ions give only a single feature at gD 5:0. The different spectra are due to different crystal field strengths. The higher charge of Tb 4+ ions results in a stronger local field compared with Eu 2+ ions.