Absence of the enhanced intra-4f transition cross section at 1.5 μm of Er3+ in Si-rich SiO2

We present measurements of the optical absorption cross section of the ⁴ I_15/2→⁴ I_13/2 transition at 1.5 μm of Er³⁺ ions embedded in SiO₂ and Si-rich oxide, using cavity ringdown spectroscopy on thin films. The peak absorption cross section for Er³⁺ embedded in Si-rich oxide (10 at. % excess Si) was found to be (8±2)×10⁻²¹ cm² at 1536 nm, similar to typical values for Er embedded in SiO₂. The data imply that the silicon nanoclusters incorporated in Si-rich oxide do not enhance the peak cross section of the Er^{3+ 4} I_15/2−⁴ I_13/2 transition by 1-2 orders of magnitude, contrary to what has been reported in earlier work.