Modification of energy transfer from Si nanocrystals to ${\mathrm{Er}}^{3+}$ near a Au thin film

The effects of a Au thin layer on the rate of energy transfer from Si nanocrystals (Si-nc’s) to ${\mathrm{Er}}^{3+}$ were studied. The energy transfer rate was found to oscillate with increasing the separation between the active layer and the Au thin film. The period of the oscillation agreed well with that of the calculated radiative decay rates of Si-nc’s at the energy transfer wavelength. The present results provide evidence that the rate of energy transfer from Si-nc’s to ${\mathrm{Er}}^{3+}$ is proportional to the photonic mode density at the energy transfer wavelength and can be controlled by controlling the photonic environment.

Figure 1

Schematic representation of the sample structure. ${\mathrm{SiO}}_2$ active layer containing Si-nc’s and Er $(\mathrm{Si}\text{−}\mathrm{nc}:\mathrm{Er}:{\mathrm{SiO}}_2)$ or Si-nc’s $(\mathrm{Si}\text{−}\mathrm{nc}:{\mathrm{SiO}}_2)$ is deposited on a ${\mathrm{SiO}}_2$ substrate. On the active layer, a ${\mathrm{SiO}}_2$ spacer layer and a Au thin layer (100 nm) is deposited.

Figure 2

(a) The PL spectra of a ${\mathrm{SiO}}_2$ film containing Si-nc’s $({\mathrm{d}}_{\mathrm{Si}}=4.1\mathrm{nm})$ and that containing Si-nc’s and Er (0.11 at. %). The broad emission band at around 1.27 eV is due to recombination of excitons in Si-nc’s, and a sharp peak at 0.81 eV arises from intra $4\text{−}f$ shell transition of ${\mathrm{Er}}^{3+}({}^{4}I_{13∕2}\to {}^{4}I_{15∕2})$. (b) PL decay curves of Si-nc’s at 1.26 eV for the sample containing and not containing Er. Inset shows a typical PL time transient of Er at 0.81 eV.

Figure 3

(a) The PL decay rates of Si-nc’s as a function of spacer thickness (closed squares). The decay rate without the Au thin film is shown by a horizontal dashed line (left axis). The solid curve represents the normalized decay rate calculated for an isotropic dipole emitting at 1.26 eV (right axis). In the inset, the PL decay curves of Si-nc’s for various spacer thickness are shown. (b) A dissipated power spectrum at 1.26 eV for an isotropic dipole positioned at the center of an active layer as a function of normalized in-plane wave vector. (c) Spacer thickness dependence of the total decay rate (solid line), the radiative rate (dashed line), the rates of energy transfer to surface plasmon modes (dotted line), and lossy wave modes (dashed dotted line). In obtaining these rates, the contribution of dipoles positioned between the active layer/substrate and the active layer/spacer interfaces were averaged.

Figure 4

(a) The PL decay curves of Si-nc’s (1.26 eV) with (closed circles) and without (open circles) Au thin films for the samples containing Si-nc’s and Er. The spacer thickness is 330 nm. (b) The PL time transients of ${\mathrm{Er}}^{3+}$ (0.81 eV) with (closed triangles) and without (open squares) Au thin films obtained for the same samples. The spacer thickness is 600 nm. The solid and dashed curves are the results of fitting (see Ref. 12).

Figure 5

The PL decay rates of a ${\mathrm{SiO}}_2$ film containing Si-nc’s (closed squares) and that containing Si-nc’s and Er (open squares) at 1.26 eV as a function of spacer thickness. The decay rates of $\mathrm{Si}\text{−}\mathrm{nc}:{\mathrm{SiO}}_2$ and $\mathrm{Si}\text{−}\mathrm{nc}:\mathrm{Er}:{\mathrm{SiO}}_2$ without Au thin films are shown by the horizontal dashed line and horizontal dotted line, respectively.

Figure 6

Energy transfer rates estimated from the time transient of Er PL (open squares) and that estimated from decay rates of Si-nc’s (closed squares) as a function of spacer thickness. The solid curve represents calculated radiative rate at 1.26 eV (right axis). Energy transfer rates estimated from Er PL and Si-nc’s PL for the sample without Au thin films are shown by the horizontal dotted and horizontal dashed lines, respectively.