Direct excitation spectroscopy of Er centers in porous silicon

Abstract
We report direct excitation of optically active Er centers in porous Si. Excitation spectroscopy performed close to the intracenter I415/2→I411/2 and I415/2→I49/2 transitions of Er3+ (4f11) ions allows us to identify two kinds of Er centers in porous Si: (i) Er diffused into porous nanograins with lower than cubic symmetry and (ii) Er centers incorporated in an amorphous silicalike matrix. The latter show much weaker thermal quenching of the Er3+ emission which decreases only by a factor of eight when the temperature is increased from 4.2 K up to 360 K.