Spectroscopy and near infrared upconversion of Er³⁺-doped TZNT glasses

In this paper we report on the near infrared (NIR) upconversion (UC) and spectroscopic properties of erbium (Er³⁺)-doped TeO₂-ZnO-Nb₂O₅-TiO₂ (TZNT) oxide glasses. Judd-Ofelt theory has been applied to investigate the intensity parameters (Ω_λ, λ=2, 4 and 6) which are used to derive radiative properties of the fluorescent levels. The different glasses present high refractive indices, low dispersion and Abbe numbers, as determined by variable angle spectroscopic ellipsometry. Under 980 nm excitation, the NIR emission profile and full width at half maximum have been studied in a broad range of Er³⁺ concentrations (0.01-3.0 mol%). On the other side, NIR UC has been obtained by exciting at 1523 nm, showing an increase of the intensity with Er³⁺ ion density in the studied range. The decay curves of the ⁴I_13/2 level exhibit single exponential nature for all the different concentrations. The lifetime of the ⁴I_13/2 level has been found to decrease (3.73-1.20 ms) after an initial increase (3.65-3.73 ms) with increasing of Er³⁺ ion concentration. The TZNT samples show broadband UC emission at 1.0 μm, which match with the band gap of silicon. This reveals that the investigated glasses could find application in photonics, for example non-linear optics and photovoltaic's.