Radiative and non-radiative transition probabilities and quantum yields for excited states of Er³⁺ in germanate and tellurite glasses

Absorption and fluorescence spectra of Er³⁺ in germanate and tellurite glasses were obtained. Spontaneous transition probabilities of the ⁴S _{3 2} and ⁴F _{9 2} to all terminal levels of Er³⁺ were calculated using the Judd-Ofelt theory and intensity parameters obtained from measured intergrated absorption coefficients. Quantum efficiencies of the ⁴S _{3 2} and ⁴F _{9 2} fluorescences were measured by the comparative method and by the use of measured decay times. Multiphonon relaxation rates for ⁴S _{3 2} → ⁴F _{9 2} and ⁴F _{9 2} → ⁴I _{9 2} were calculated using the experimental data. The average rate for ⁴S _{3 2} → ⁴F _{9 2} in germanate is 1.16 × 10⁵ sec^-1 and in tellurite is 1.60 × 10⁴ sec^-1, and the rate for ⁴F _{9 2} → ⁴I _{9 2} is 2.85 × 10⁵ sec^-1 in germanate and 2.33 × 10⁵ sec^-1 in tellurite. The higher rates in germanate glasses are explained by the stronger interaction of the glass phonons with the electronic states of Er³⁺ in germanate than in tellurite glasses. This also explains the higher quantum yield of the visible fluorescence of Er³⁺ in tellurite glasses compared to other glasses.