Near-infrared emission and upconversion in Er3+-doped TeO2–ZnO–ZnF2 glasses

We have investigated the near infrared emission and upconversion of Er3+ ions in two different compositions of glasses based on TeO2, ZnO, and ZnF2 for different ErF3 concentrations (0.5, 1, 2, and 3 wt%). Judd–Ofelt intensity parameters have been determined and used to calculate the radiative transition probabilities and radiative lifetimes. The infrared emission at around 1532 nm corresponding to the 4I13/2→4I15/2 transition is broader by nearly 30 nm if compared to silica based glasses. The stimulated emission cross section is higher for the glass with the lowest content of ZnF2 which also shows higher values of the figure of merit for bandwidth. On the other hand, the lifetimes of the excited states are longer for the glass with the highest content of ZnF2. Green and red emissions corresponding to transitions (2H11/2,4S3/2)→4I15/2 and 4F9/2→4I15/2 have been observed under excitation at 801 nm and attributed to a two photon process. The temporal evolution of the green emission suggests the presence of excited state absorption and energy transfer upconversion processes to populate the 4S3/2 level. In the case of the red emission, its increase as ErF3 concentration increases together with its temporal behavior indicate that for ErF3 concentrations higher than 0.5 wt%, level 4F9/2 is populated by multiphonon relaxation from level 4S3/2 and energy transfer processes.