This paper investigates the interaction between Si nanoclusters ͑Si-nc͒ and Er in SiO 2 , reports on the optical characterization and modeling of this system, and attempts to clarify its effectiveness as a gain material for optical waveguide amplifiers at 1.54 m. Silicon-rich silicon oxide layers with an Er content of 4 -6 ϫ 10 20 at./ cm 3 were deposited by reactive magnetron sputtering. The films with Si excess of 6 -7 at. %, and postannealed at 900°C showed the best Er 3+ photoluminescence ͑PL͒ intensity and lifetime, and were used for the study. The annealing duration was varied up to 60 min to engineer the size and density of Si-nc and optimize Si-nc and Er coupling. PL investigations under resonant ͑488 nm͒ and nonresonant ͑476 nm͒ pumping show that an Er effective excitation cross section is similar to that of Si-nc ͑ϳ10 −17 -10 −16 cm 2 ͒ at low pumping flux ͑ϳ1016 -10 17 cm −2 s −1 ͒, while it drops at high flux ͑Ͼ10 18 cm −2 s −1 ͒. We found a maximum fraction of excited Er of about 2% of the total Er content. This is far from the 50% needed for optical transparency and achievement of population inversion and gain. Detrimental phenomena that cause depletion of Er inversion, such as cooperative up conversion, excited-stated absorption, and Auger deexcitations are modeled, and their impact in lowering the amount of excitable Er is found to be relatively small. Instead, Auger-type short-range energy transfer from Si-nc to Er is found, with a characteristic interaction length of 0.4 nm. Based on such results, numerical and analytical ͑Er as a quasi-two-level system͒ coupled rate equations have been developed to determine the optimum conditions for Er inversion. The modeling predicts that interaction is quenched for high photon flux and that only a small fraction of Er ͑0.2-2 %͒ is excitable through Si-nc. Hence, the low density of sensitizers ͑Si-nc͒ and the short range of the interaction are the explanation of the low fraction of Er coupled. Efficient ways to improve Er-doped Si-nc thin films for the realization of practical optical amplifiers are also discussed.

The present article deals with the optimized processing conditions leading to the highest density of Si nanoclusters which play the role of sensitizing centers for the nearby Er ions within a silica matrix. The layers were obtained by reactive magnetron sputtering under a plasma of Ar mixed to different rates of hydrogen, and were subsequently annealed at various temperatures. The increase of the dilution degree of the Ar plasma with hydrogen was found to multiply the nucleation sites whose density foreshadows that of the Si nanoclusters formed upon annealing. Both hydrogen content and annealing temperature govern the growth of the clusters. The maximum density of efficient sensitizing centers was obtained for hydrogen rate in the plasma of 50% and annealing at 900 °C. This has directly led to the enhancement of the coupling rate between the Si nanoclusters and the Er ions, as reflected by the ten times increase of the proportion of optically active ions, compared to that for standard conditions. In parallel, the lifetime emission of the active Er ions was found to continuously improve with the annealing temperature and has reached values exceeding 7 ms.