Broadband fluorescence emission of Eu^3+ 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.