Spectroscopy and gain in $Al_2O_3:Er$ waveguides

The spectroscopic properties of the $Al_2O_3:Er$ layers were investigated by lifetime measurements. Typical Bernoulli-type decay curves were found, with an increasingly fast non-exponential initial component for higher Er concentrations, which results from enery-transfer upconversion between neighbouring Er ions. The exponential tail at long decay times exhibits an asymptotic lifetime which decreases from 7ms for Er concentrations of ~2x$10^{19} cm^{-3}$ down to 2 ms for Er concentrations of ~4x$10^{20} cm^{-3}$. This behavior may result from either pair-induced energy-transfer upconversion or quenching by impurity ions present in the metallic Er target used for sputtering. We conclude that at least two different types of quenching mechanisms are present in the decay