Maximum fraction of Er3+ ions optically pumped through Si nanoclusters

By quantifying the amount of excited Er ions and considering the interaction distance between Si nanoclusters (Si-ncs) and the nearby Er ions, we were able to determine the maximum excitable Er concentration, when indirectly pumped through the Si-ncs. Our study was carried out on silica layers codoped with Si clusters and Er ions, grown by reactive magnetron sputtering. Si-rich silica layers were formed with different amounts of Si excess and doped to a wide range of Er concentrations. Thermal treatments were performed at 900 °C for different durations to maximize the Er emission at 1540 nm. The saturation limit of Er ions optically excitable through the Si-ncs was found about 3% of the total concentration. Simulations were carried out in order to explain this low value. The modelization takes into account the spatial distribution of the Er population, the measured size and density of Si clusters and the short-range character of the interaction between Er and Si-ncs. The small excitable fraction thus obtained appears as the ultimate intrinsic limitation to attain very high optical efficiency in such structures.