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

We present measurements of the optical absorption cross section of the I15∕24→I13∕24 transition at 1.5μm 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 (10at.% excess Si) was found to be (8±2)×10−21cm2 at 1536nm, 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 Er3+ I15∕24−I13∕24 transition by 1-2 orders of magnitude, contrary to what has been reported in earlier work.