Enhancement of near-infrared emission of Er³⁺ in tellurite glasses by reducing the phonon energy with Bi₂O₃ content

Erbium ions, significant rare-earth ions used in the preparation of high-power near-infrared, have extensive applications in near-infrared lasers, fiber amplifiers, and radar. As a heavy metal glass, tellurite glass boasts stable physical and chemical properties, high mechanical strength, a large refractive index, and high solubility of rare-earth ions. Consequently, in this study, we modulate the tellurite glass grid to enhance the intensity of near-infrared emission from erbium ions in the classic TeO₂–ZnO–Na₂O (TZN) glass system. The local coordination field environment of erbium ions is optimized by the alternating grouping of bismuth oxide with low phonon energies. Thermal analysis indicates that the addition of an appropriate amount of bismuth oxide can improve the thermal stability of the glass and effectively reduce the content of OH⁻ in the glass system. Upon replacing TeO₂ with Bi₂O₃, the 1.5 μm emission of erbium ions is enhanced by 38.9%, with a maximum emission cross section of 0.84 × 10^–20 cm². Raman spectra reveal that after the introduction of bismuth oxide, most of the vibration modes of the system shift to low wavenumber sidebands, effectively suppressing the non-radiative transition in the ⁴I_13/2 energy level. The full width at half maximum (FWHM) × emission cross section (σ_e) reaches its maximum value of 58.958 when the concentration of Bi₂O₃ replacing Na₂O is 6 mol%, which is greater than other glasses such as tellurite, silicate, and phosphate glasses. All these results suggest that the newly created bismuth tellurite glass, characterized by excellent fiber-forming properties, has potential applications for near-infrared lasers.