Distance dependent interaction as the limiting factor for Si nanocluster to Er energy transfer in silica

Si excess, Er content, and processing parameters have been optimized in a series of cosputtered oxide layers for maximizing Er emission and lifetime. The amount of excited Er as a function of the incident photon flux has been quantified for resonant $\left(488\mathrm{nm}\right)$ and nonresonant $\left(476\mathrm{nm}\right)$ excitations. Results show that a maximum of 3.5% of Er ions is excitable through the Si nanoclusters (Si-nc). This low value cannot be explained only by cooperative upconversion and/or excited state absorption. A short range $\left(0.5\mathrm{nm}\right)$ distance dependent interaction model is developed that accounts for this low Er population inversion. The model points to the low density of Si-nc $[(3–5)\times {10}^{17}{\mathrm{cm}}^{-3}]$ as the ultimate limiting step for indirect Er excitation in this system.