Optical spectra and relaxation of Eu⁺³ in germanate glasses

Optical absorption and emission spectra of Eu⁺³ in germanate glass, as well as the fluorescence decay time of ⁵D₀ → underover(∑, 0, 6) ⁷F_i were measured. Oscillator strengths up to 360 nm were calculated and compared with those of Eu⁺³ in various glasses. It was found that the hypersensitive transitions ⁷F₀→⁵D₂ and ⁵D₀→⁷F₂ were stronger in germanate than in silicate or phosphate glasses, owing to covalency effects. Transition rates and efficiencies from ⁵D₀ to the ground levels and ⁵D₁→⁵D₀ were calculated. Fluorescence was observed from the ⁵D₂, ⁵D₃, ⁵L₆ levels in addition to that from ⁵D₀ and ⁵D₁ observed in phosphate and silicate glasses. The appearence of fluorescence from the higher levels is attributed to the influence of the lower phonon energy of germanate glasses.