Energy transfer in Er-dopedSiO2sensitized with Si nanocrystals

Abstract

We present a high-resolution photoluminescence study of Er-doped ${\text{SiO}}_{2}$ sensitized with Si nanocrystals (Si NCs). Emission bands originating from recombination of excitons confined in Si NCs, internal transitions within the $4f$-electron core of ${\text{Er}}^{3+}$ ions, and a band centered at $\ensuremath{\lambda}\ensuremath{\approx}1200\text{ }\text{nm}$ have been identified. Their kinetics were investigated in detail. Based on these measurements, we present a comprehensive model for energy-transfer mechanisms responsible for light generation in this system. A unique picture of energy flow between the two subsystems was developed, yielding truly microscopic information on the sensitization effect and its limitations. In particular, we show that most of the ${\text{Er}}^{3+}$ ions available in the system are participating in the energy exchange. The long-standing problem of apparent loss of optical activity in the majority of Er dopants upon sensitization with Si NCs is clarified and assigned to the appearance of a very efficient energy exchange mechanism between Si NCs and ${\text{Er}}^{3+}$ ions. Application potential of ${\text{SiO}}_{2}:\text{Er}$, sensitized by Si NCs, was discussed in view of the newly acquired microscopic insight.