Non-radiative sub-microsecond recombination of excited Er3+ ions in SiO2 sensitized with Si nanocrystals

Temporal aspects of recombination and energy transfer processes in Er-doped SiO2 sensitized with Si nanocrystals (Si-nc's) were investigated by luminescence and excitation spectroscopy using time-correlated photon counting. This detection mode allows that emissions of very different intensities and dynamics may be investigated simultaneously, without loss of time resolution or amplitude deformation. In this way, components with decay constants ranging from nano- to milliseconds were identified in the luminescence bands of Si-nc's, Er3+ ions, and defects. We postulate to relate these to recombination processes originating from isolated Er3+ ions and Er3+ ions located inside or in direct vicinity of Si-nc's, with dynamics in the milli- and microsecond, and nanosecond range, respectively. In this way, a unique picture of the mutual relation between the two subsystems of Er3+ ions and Si-nc's, and truly microscopic information on the sensitization effect is obtained. Based on this new information, we conclude on a strong enhancement of non-radiative recombination of Er3+ upon sensitization with Si-nc's and put forward a complete description of Si-nc's as sensitizers of SiO2:Er system, where all the Er3+ ions available in the system are accounted for.