Survey of optical and fluorescence traits of Tm³⁺-doped alkali/mixed alkali oxides constituting B₂O₃-BaO-ZnO-LiF glasses for 0.45 μm laser and 1.46 μm fiber amplifier

For six 1 mol% Tm³⁺-doped B₂O₃-BaO-ZnO-LiF glasses containing single and mixed alkali oxides (fabricated by melt-cast approach), optical absorption, and visible and near-infrared (NIR) fluorescence features including visible luminescence decay times were explored. Optical band gaps, Urbach energy, and two-photon absorption coefficients were evaluated for all studied glasses. Judd–Ofelt (J–O) analysis from absorption spectra was performed to compute Tm³⁺: 4f–4f transitions J–O parameters Ω_λ (λ = 2, 4, 6), and utilizing Ω₂, Ω₄ and Ω₆ values radiative transition probabilities (A_R), branching ratios (β_R), and radiative lifetimes (τ_R) for all Tm³⁺ ion's excited levels were assessed. For obtained intense blue emission band (454 nm) upon 358 nm excitation, various parameters considered in developing visible laser systems were calculated. Tm³⁺: Na ions having sample exhibits high A_R, highest peak emission cross-section (σ_max^em) (=5.89 × 10^–21 cm²) and gain bandwidth(σ_max^em × Δλ_eff) (=9.69 × 10^–27 cm³) for ¹D₂→³F₄ luminescence transition in all glasses for a favorable blue lasing process. All emission decay curves of the ¹D₂ upper level showed nonexponential nature. Commission Internationale de l'éclairage (CIE) coordinates, color purity, and luminous efficiency of radiation were derived from visible fluorescence spectra, and attained CIE (x,y) coordinates values reflect the purplish-blue light region. Under direct optical pumping of ³H₆→³H₄ transition using 808 nm laser diode, NIR fluorescence spectra exhibit a wideband within 1.3–1.6 μm spectral range peaked at 1.46 μm (³H₄→³F₄ transition). NIR emissions effective bandwidth (Δλ_eff) was varied relying on different alkali oxides. Δλ_eff ~ 121 nm was deduced for Tm³⁺: Li ions comprising glass with large σ_max^em (=1.832 × 10^–21 cm²), high(σ_max^em × Δλ_eff) (=2.22 × 10^–26 cm³), and optical gain (=12.608 × 10^–25 cm²s) for ³H₄→³F₄ emission transition and its gain profile wraps the entire S-optical communication band range for efficient broadband amplification purpose in wavelength-division multiplexing systems.