High-Resolution Line Width Measurement of Single CdSe Nanocrystals at Long Time Scales

Band-edge photoluminescence from single CdSe/CdZnS nanocrystals was analyzed using a confocal Fabry-Perot spectrometer with long exposure times. Due to spectral diffusion, direct detection of the line shape was not possible. However, the contrast observed in the resulting signal provided a rigorous upper bound to the single nanocrystal line width as low as 20.7 +/- 0.5 mu eV. This result is in excellent agreement with an asymptotic upper limit to the spectral diffusion broadened line width found at millisecond time scales, extending this time scale by 4 orders of magnitude. This indicates that spectral diffusion commonly observed at long time scales results from a physical process different from that/those responsible for the asymptotic limit.