Broadband fluorescence emission of Eu³⁺ doped germanotellurite glasses for fiber-based irradiation light sources

Eu³⁺ doped fiber-based germanotellurite (NZPGT) glasses with medium-low maximum phonon energy of 782 cm^-1 have been fabricated and characterized. Judd-Ofelt intensity parameters Ω₂ (6.25 × 10^-20 cm²) and Ω₄ (1.77 × 10^-20 cm²) indicate a high asymmetrical and covalent environment around Eu³⁺ in the optical glasses. The spontaneous emission probability of the dominant transition ⁵D₀→⁷F₂ peaking at 612.5 nm and the corresponding maximum stimulated emission cross-section were derived to be 445.7 s^-1 and 2.05 × 10^-21 cm², respectively, confirming the effectiveness of the red fluorescence emission. The quantum yield was derived to be 12% under 391 nm LED excitation, and approximately 88% photons have been demonstrated in wavelength range of 600-720 nm, indicating that Eu³⁺ doped NZPGT glasses under proper excitation conditions are promising optical materials for fiber-based irradiation light sources that are competent to activate diverse photodynamic therapy photosensitizers.