Spectroscopy evaluation of Nd3+-activated novel CdO–V2O5–ZnO–B2O3 inverted glasses for near infrared laser applications

Abstract

Nd3+-activated CdO–V2O5–ZnO–B2O3 (CVZB) inverted glasses with chemical composition of 80–5.0-2.5–12.5 mol%, respectively, were prepared by melt-quenching to analyze their optical spectroscopy features by applying the Judd-Ofelt (JO) theory. The Nd3+ content was changed from 0.4 up to 4.0 mol%. The structural characterization carried out by X-ray diffraction patterns and Raman spectroscopy, confirmed the amorphous nature for doping contents up to 4.0 mol% of Nd3+. The direct (Egdir) and indirect (Egind) band gap obtained from the absorption spectra, showed values of 2.76 ± 0.12 and 2.50 ± 0.10 eV, respectively, without significative changes by the Nd3+ doping variations. Such band gap energy values are suitable to allow the Nd3+ emissions centered at 878, 1060 and 1332 nm, corresponding to the 4F3/2 → 4I9/2,11/2,13/2 transitions, respectively. The Nd3+ emission intensity reached the optimum at 2.8 mol% of Nd3+. At larger Nd3+ concentrations, the emission is gradually quenched due to cross-relaxation processes. These processes were dominated by electric dipole-dipole interactions within Nd3+-Nd3+ clusters, as suggested by the Inokuti-Hirayama model and critical interaction distance. The experimental branching ratios (βexp) were stables up to 1130 mW of 808 nm laser excitation, with values of (4F3/2 → 4I9/2) βexp = 0.28, (4F3/2 → 4I11/2) βexp = 0.56, and (4F3/2 → 4I13/2) βexp = 0.16. The JO parameters for the optimal emitting glass (2.8 mol% of Nd3+) obtained from least-square fitting between theoretical (fcal) and experimental (fexp) oscillator strengths, were Ω2 = 5.31 × 10−20, Ω4 = 2.81 × 10−20 and Ω6 = 3.34 × 10−20 cm2. The stimulated cross-section peak (σp), obtained from the JO parameters, resulted to be σp = 1.21 × 10−20 and 3.50 × 10−20 cm2 for the 4F3/2 → 4I9/2 and 4F3/2 → 4I11/2 transitions, respectively. The radiative (τR) and experimental (τexp) lifetimes led to quantum yield value of 0.49. Finally, laser parameters for the 4F3/2 → 4I11/2 emission, such as bandwidth (σPEMI × Δλem) and optical gain (σPEMI × τR) were calculated from the emission cross-section peak (σPEMI, 1061 nm), resulting values of 165 × 10−27 cm3 and 37 × 10−25 cm2s, respectively.