Upconversion spectroscopy of Al₂O₃:Er³⁺

The spectroscopic properties of $Al_2O_3:Er^{3+}$ thin films have been investigated by lifetime measurements. The luminescence decay curves show an initial non-exponential component, followed by an exponential tail, whose decay time decreases with increasing $Er^{3+}$ concentration. This behavior can be described with good accuracy by a microscopic treatment that takes into account both energy migration and energytransfer upconversion among $Er^{3+}$ ions. Parameters such as the migration mean time τ$_0$ and the donor-acceptor transfer probability CDA are derived. We show that, in the concentration range of interest for waveguide amplifiers at 1.5 μm, upconversion occurs mostly in the static regime.