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 (488nm) and nonresonant (476nm) 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 (0.5nm) 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)×1017cm−3] as the ultimate limiting step for indirect Er excitation in this system.