Resonant energy transfer from silicon nanocrystals to iodine molecules

The electronic excitation energy transfer between excitons in silicon nanocrystal assemblies and iodine molecules in an organic solution is studied. From the time-resolved photoluminescence the rate of the energy transfer is found to increase with approaching a wavelength region, where the photoluminescence spectrum of nanocrystals overlaps the absorption spectrum of iodine molecules, and with increasing the radiative recombination rate of nanocrystals. The energy-transfer rate is also found to depend on the concentration of iodine molecules. This dependence is well explained by Förster-type dipole-dipole interaction mechanism in which the diffusion of the assemblies and molecules is taken into consideration.

Figure 1

(Color online) PL spectra of a porous Si powder dispersed in trichloroethylene with adding iodine molecules. The concentration of iodine solutions is varied from 0 to $5.4\times {10}^{-4}\text{mol}/\text{l}$. The dashed line represents an absorption spectrum of iodine molecules (right axis).

Figure 2

(Color online) (a) Time-resolved PL spectra of a porous Si powder dispersed in trichloroethylene with (dashed lines) and without adding iodine molecules (solid lines). The gate time is 60 ns. The data taken with various delay time from the excitation pulse of 0.08, 0.3, 2, and $6\mu \text{s}$ are shown. The absorption peak wavelength of iodine molecule is shown by the vertical dashed line. (b) PL decay curves detected at 567 nm (open symbols) and at 700 nm (closed symbols). The concentration of iodine molecules is varied from 0 to $5.4\times {10}^{-4}\text{mol}/\text{l}$.

Figure 3

(Color online) Time-resolved PL spectra of a porous Si powder in trichloroethylene with adding iodine molecules divided by the PL strengths without adding iodine $\left({\text{I}}_{\text{w}}/{\text{I}}_{\text{wo}}\right)$. The gate time is 60 ns. The data taken with various delay time from the excitation pulse of 0.08, 0.3, 2, and $6\mu \text{s}$ are shown. The concentrations of iodine solutions are (a) $0.4\times {10}^{-4}$, (b) $1.6\times {10}^{-4}$, and (c) $5.4\times {10}^{-4}\text{mol}/\text{l}$.

Figure 4

(Color online) ${\text{I}}_{\text{w}}/{\text{I}}_{\text{wo}}$ as a function of delay time detected at 567 and 700 nm. The concentrations of iodine solutions are $1.6\times {10}^{-4}$ (closed squares) and $5.4\times {10}^{-4}$ (open triangles) mol/l.

Figure 5

(Color online) (a) PL decay rate of porous Si dispersed in a solution with iodine molecules as a function of the emission wavelength. The concentrations of iodine solutions are 0, $1.6\times {10}^{-4}$, and $5.4\times {10}^{-4}\text{mol}/\text{l}$. (b) Energy-transfer rate as a function of emission wavelength. The concentrations of iodine solutions are $0.4\times {10}^{-4}$, $1.6\times {10}^{-4}$, and $5.4\times {10}^{-4}\text{mol}/\text{l}$.

Figure 6

(Color online) Energy-transfer rate detected at 550 (open squares) and 650 nm (closed squares) as a function of iodine concentration. Dashed and solid lines represent theoretical curves calculated from Eq. (1) for $R_0=2.18\text{nm}$ and $a=0.45\text{nm}$.