A detailed investigation of the excitation mechanisms of the ⁴I_13/2-⁴I_15/2 intra-4f-shell luminescence of Er³⁺ ions near 1.5 μm in silicon-rich silicon oxide (SRSO) is reported. SRSO:Er was produced by high dose implantation of Si⁺ ions into SiO₂ layers grown on silicon, followed by Er⁺ implantation at an energy of 800 keV. Samples were thermally annealed up to 1100^oC to create different types of defects and Si-nanocrystals (nc-Si). Photoluminescence excitation (PLE) spectra were obtained using optical parametric oscillator (OPO) and Ti:Sapphire laser in the range 420-680 and 720-830 nm, respectively.
The results show that in SRSO:Er two mechanisms of excitation are in competition: a resonant one and via defects. The resonant channel of excitation of Er³⁺ 4f-shell which gives a maximum luminescence yield for Er doped silica without additional Si is suppressed by the silicon excess related defects; resonant peaks disappear with increasing of annealing temperature of SRSO. We suggest that the dominant factors, which limit the excitation efficiency of Er³⁺ in SRSO, are distance dependence of the transfer rate and little spectral overlap of the interacting states. Employing density of states function for nc-Si, Er³⁺ absorption function and spectral overlap integral, the quantitative estimation of overall efficiency of the system nc-Si:Er³⁺ for multipole interaction between localized in nc-Si (or nc-Si/SiO₂ interface) e-h pairs and 4f-states of Er³⁺ is presented. The dependence of the Er³⁺ emission on excitation duration were also studied. For one electron-hole pair being generated by excitation pulse we show that one nc-Si can excite only one or less of Er³⁺ ions in its vicinity.

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