Up-conversion and down-shifting emission traits of Er³⁺-doped CdO–V₂O₅–ZnO–B₂O₃ novel inverted glasses for photonic applications

Er³⁺-doped CdO–V₂O₅–ZnO–B₂O₃ (CVZB-Er) inverted glasses were synthesized by the melt-quenching method. X-ray diffraction (XRD) patterns showed an amorphous structure in all Er³⁺ doping ranges. This fact was verified by the line shape of Raman spectra, which revealed two broad vibrational bands attributed to V₂O₅ and B₂O₃ glass former species. The direct optical band gap (E_g^d) values were found around 2.74 eV, without tendency with Er³⁺ concentration. Under 980 nm laser excitation, the down-shifting emission spectra exhibited the featured near-infrared Er³⁺: ⁴I_13/2 → ⁴I_15/2 emission band. Meanwhile, the upconverting (UC) emission spectra, with color purities up to 97 %, displayed the well-known green and red emission bands related to relaxations from the (²H_11/2, ⁴S_3/2) and ⁴F_9/2 excited states to the ⁴I_15/2 ground one, respectively. This process is dominated by a linear decay mechanism, as revealed by the dependence of the intensity versus the excitation laser power. The Judd-Ofelt (JO) parameters, obtained by the least-square method from the experimental and calculated oscillator strengths, resulted in Ω₂ = 6.43 × 10⁻²⁰ cm², Ω₄ = 0.96 × 10⁻²⁰ cm² and Ω₆ = 1.53 × 10⁻²⁰ cm² for the CVZB glass activated with 2.8 mol% of Er³⁺. Such values are close to those reported in other glass systems. Moreover, the radiative transitions arising from the ⁴I_13/2 and ⁴S_3/2, states to the ⁴I_15/2 ground one presented radiative branching ratio (β_R) values higher than 0.6, and total radiative transfer probabilities A_T (⁴I_13/2 →⁴I_15/2) = 782.46 s⁻¹ and A_T (⁴S_3/2 →⁴I_15/2) = 10248.56 s⁻¹. For the ⁴I_13/2→⁴I_15/2 emission transition, laser parameters such as the stimulated emission cross-section (σ_em(λ) = 1.57 × 10⁻²⁰ cm²), gain bandwidth (σ_em(λ) × Δλ_em=9.3 × 10⁻²⁶ cm³), optical gain (σ_em(λ) × τ_R=2.0 × 10⁻²³ cm²s) and quantum yield (η=0.33) were calculated.