Optical and visible and near-infrared fluorescence aspects of Er³⁺, Tm³⁺, and Nd³⁺-doped B₂O₃-rich glasses for fiber amplifiers and NIR lasers

For synthesized each 1 mol% Er³⁺, Tm³⁺, and Nd³⁺-doped borate-rich glasses, optical and luminescence traits including fluorescence decay dynamics were explored. For Er³⁺: glass, at 1.4–1.65 μm range a wide NIR (near-infrared) luminescence band centered at 1.531 μm (⁴I_13/2 → ⁴I_15/2) and in Tm³⁺: glass, at 1.35–1.6 μm span a broad NIR fluorescence band centered at 1.458 μm (³H₄→³F₄) are obtained by 980 nm LD (laser diode) pumping (⁴I_15/2 → ⁴I_11/2) and 808 nm LD excitation (³H₆→³H₄) separately. Under 808 nm LD pumping (⁴I_9/2 → ⁴F_5/2+²H_9/2), in Nd³⁺: glass, three emission bands peaked at 0.901 μm (⁴F_3/2 → ⁴I_9/2), 1.057 μm (⁴F_3/2 → ⁴I_11/2), and 1.329 μm (⁴F_3/2 → ⁴I_13/2) respectively are observed and in all such emissions, comparably the one obtained from transition ⁴F_3/2 → ⁴I_11/2 is highly intense. For acquired main visible and NIR emissions, Δλ_eff (effective bandwidth), by Füchtbauer–Ladenburg approach σ_emi (stimulated emission cross-section), gain bandwidth, and optical gain are evaluated. 75.73 nm, 113.67 nm, and 57.37 nm are the Δλ_eff values for Er³⁺: ⁴I_13/2 → ⁴I_15/2, Tm³⁺: ³H₄→³F₄, and Nd³⁺: ⁴F_3/2 → ⁴I_13/2 transitions accordingly. Using McCumber's theory, the calculated peak σ_emi for Er³⁺: ⁴I_13/2 → ⁴I_15/2 and Nd³⁺: ⁴F_3/2 → ⁴I_9/2 transitions are 1.495 × 10–20 cm² and 0.5556 × 10–20 cm², respectively. ⁴I_13/2 → ⁴I_15/2 transition gain cross-section spectra reveals C-band amplification at P (population inversion) = 50% in Er³⁺: glass, whereas at P = 30% for ⁴F_3/2 → ⁴I_9/2 transition gain cross-section is positive for lasing action at ∼0.9 μm in Nd³⁺: glass. All analyzed NIR luminescence outcomes reveal that studied glasses could be potential gain media for C-, S-, and O-bands fiber amplifiers and solid-state lasers.