Monitoring Surface Charge Movement in Single Elongated Semiconductor Nanocrystals

We demonstrate a universal correlation between the spectral linewidth and position of the excitonic transition in the spectral jitter observed from single elongated colloidal quantum dots. Breaking the symmetry of electron and hole confinement as well as of the spatial directions for surface charge diffusion enables us to microscopically track meandering surface charges, providing a novel probe of the particle's nanoenvironment. Spectral diffusion exhibits only a weak temperature dependence, which allows us to uncover the single particle homogeneous linewidth of 50 meV at room temperature.

Figure 1

Two PL spectra measured from a single elongated $\mathrm{C}\mathrm{d}\mathrm{S}\mathrm{e}/\mathrm{C}\mathrm{d}\mathrm{S}$ NC at 5 K at different times. The presence of surface charge results in spectral shifts through the QCSE, and spatial charge oscillations lead to line broadening. The sketch illustrates the influence of surface charge: depending on the proximity to the emitting CdSe core, which determines the peak position, the same spatial amplitude of oscillations (arrows) results in different spectral linewidths. The inset shows a TEM image of elongated NCs.

Figure 2

(a) Spectral jitter of the single NC emission at 5 K. (b) Dependence of PL peak position (squares) and linewidth (circles) on time.

Figure 3

Correlation between the linewidth and the PL peak position for a single NC showing the raw data from Fig. 2 (open squares). Selection of spectra that do not shift over 3 s results in the solid small squares. The large squares show the statistical average of the single particle correlation. The inset displays the histogram of spectral shifts from one spectrum to the next, with a Gaussian fit.

Figure 4

Temperature dependence of linewidth-peak shift correlations. The data of five single NCs are shown for each temperature. The solid line represents the QCSE calculated for a single charge moving along the long axis of the NC.