Spectroscopic investigations of 1.06 µm emission and time resolved Z-scan studies in Nd³⁺-doped zinc tellurite based glasses

Zinc tellurite based glasses (TZNbTiNd: TeO₂ + ZnO + Nb₂O₅ + TiO₂) doped with various Nd³⁺ concentrations (0.01, 0.05, 0.1, 0.5, 1.0, 1.5 and 2.0 mol% Nd₂O₃) were prepared and characterized through absorption, emission and decay rate measurements. Judd-Ofelt intensity parameters were derived from the absorption spectrum and used to calculate the radiative properties for the ⁴F_3/2 → ⁴I_J/2 (where J = 9, 11 and 13) transitions of Nd³⁺ ions. Strong near infrared emission at 1.062 µm (⁴F_3/2 → ⁴I_11/2) has been obtained for all the glasses upon 808 nm diode laser excitation. The decay times from ⁴F_3/2 level is found to be quite single exponential for different concentrations of Nd³⁺ ions with a shortening of lifetime with increasing concentration. In these measurements, the electronic refractive index variation is associated with the difference in the polarizabilities (Δα_p) of the Nd³⁺ ion in its ground and excited states. The results indicate that in tellurite glasses, Δα_p is relatively very high (4 × 10⁻²⁵ cm³) compared to other Nd³⁺-doped glasses. We also measured the imaginary part of the non-linear refractive index (n₂′′) due to absorption saturation. Hence, the spectroscopic results indicate that the investigated glasses are potentially applicable as a 1062 nm laser host as well as optical devices.