Spectroscopic analysis of Nd3+-doped cadmium-vanadate invert glasses for near-infrared laser applications

Nd3+ activated CdO-V2O5 invert glasses were synthesized by the well-stablished melt quenching technique, using starting proportions of 95.0 and 5.0 mol% of CdO and V2O5, respectively. The XRD patterns revealed that the glass system remains amorphous up to 4.0 mol% of Nd3+. Such fact was mainly attributed to the low V2O5 content, which avoided the segregation of additional phases. The minimal addition of 0.1 mol% of Nd3+ reduced the direct and indirect glass bandgap energies from 2.79 to 2.66 eV, and from 2.48 to 2.13 eV, respectively. For higher Nd3+ contents, the bandgap energy was recovered, reaching values of 2.78 and 2.40 eV for direct and indirect allowed transitions, respectively. This fact was associated with a Burstein-Moss like effect, observed in semiconductors highly doped. The tail of the absorption edge revealed that the Urbach energy systematically grows with the addition of Nd3+, because of the creation of localized states into the bandgap. The Judd-Ofelt (JO) parameters obtained by least-square method from the experimental and theoretical oscillator strengths, were found in the Omega(2) = 5.24-11.04 x 10(-20) cm(2), Omega(4) = 2.26-4.47 x 10(-20) cm(2), and Omega(6) = 2.85-6.28 x 10(-20) cm(2) range. Such values are close to those reported in other popular glass systems. The stimulated emission cross-section peak (sigma(p)) values calculated for the glass sample doped with 2.0 mol% resulted to be 0.26 x 10(-20) cm(2) (Nd3+: F-4(3/2) -> I-4(9/2)) and 0.81 x 10(-20) cm(2) (Nd3+: F-4(3/2) -> I-4(11/2)). The Nd3+ emission spectra, recorded upon 585 nm excitation (Nd3+: I-4(9/2) -> (4)G(5/2) + (2)G(7/2)), showed the near-infrared Nd3+ emission bands at 881 nm (Nd3+: F-4(3/2) -> I-4(9/2)), 1063 nm (Nd3+: F-4(3/2) -> I-4(11/2)) and 1341 nm (Nd3+: F-4(3/2) -> I-4(13/2)), being dominated for that coming from the Nd3+: F-4(3/2) -> I-4(11/2) transition. The overall emission reached the optimum intensity at 2.0 mol% of Nd3+, with a maximum quantum efficiency (eta(QE)) of 0.23. From the emission spectra important laser parameters such as gain bandwidth (sigma(EMI)(lambda(p)) x Delta lambda(em)) and optical gain (sigma(EMI)(lambda(p)) x tau(R)), were determined for the sample with the highest eta(QE) value. The sigma(EMI)(lambda(p)) x Delta lambda(em) values resulted to be 11.3 and 32.0 x 10(-27) cm(3) for the Nd3+: F-4(3/2) -> I-4(9/2), (11/2) transitions, respectively. The sigma(EMI)(lambda(p)) x tau(R) parameter values were 11.1 and 35.3 x 10(-25) cm(2)s for Nd3+: F-4(3/2) -> I-4(9/2,11/2) transitions, respectively. The Inokuti-Hirayama model suggested that the Nd3+ cross-relaxation process might be dominated by an electric dipole-dipole interaction, inside Nd3+-Nd3+ clusters.

Automated summary

Nd3+ activated CdO-V2O5 invert glasses were synthesized by melt quenching. Addition of Nd3+ affected the bandgap energies of the glass, with low concentrations decreasing the energy and higher concentrations recovering it. The emission spectra showed dominant transitions at specific wavelengths, with maximum quantum efficiency at 2.0 mol% Nd3+.