Energy level decay and excited state absorption processes in erbium-doped tellurite glass

The fundamental excited state decay processes relating to the 4I11/2 → 4I13/2 transition in singly Er3+-doped tellurite (TZNL) glass have been investigated in detail using time-resolved fluorescence spectroscopy. Selective laser excitation of the 4I11/2 energy level at 970 nm and selective laser excitation of the 4I13/2 energy level at 1485 nm has established that energy transfer upconversion by way of a dipole-dipole interaction between two excited erbium ions in the 4I13/2 level populates the 4I11/2 upper laser level of the 3 m transition. This upconversion has been analyzed for Er2O3 concentrations between 0.5 mol. and 2.2 mol. . The 4I13/2 and 4I11/2 energy levels emit luminescence with peaks located at 1532 nm and 2734 nm, respectively, with radiative decay efficiencies of 65 and 6.8 for the higher (2.2 mol. ) concentration sample. The low 2.7 m emission efficiency is due to the non-radiative decay bridging the 4I11/2 → 4I13/2 transition and energy transfer to the OH- groups in the glass. Excited state absorption was observed to occur from the 4I13/2 and 4I11/2 levels with peak absorptions occurring at 1550 nm and 971 nm, respectively. The decay time of the 4I11/2 excited state decreased with an increase in the Er3+ concentration, which related to energy transfer to OH- ions that had a measured concentration of 6.6 1018 cm-3. Results from numerical simulations showed that a population inversion is reached at a threshold pumping intensity of ∼80 kW cm-2 for a cw laser pump at 976 nm if [Er3+] ≥ 1.2 × 1021 cm-3 (or [Er 2O3] ≥ 2.65 mol. ) without OH- impurities being present. © 2011 American Institute of Physics.Laércio Gomes, Michael Oermann, Heike Ebendorff-Heidepriem, David Ottaway, Tanya Monro, André Felipe Henriques Librantz and Stuart D. Jackso