Bunching and antibunching in the fluorescence of semiconductor nanocrystals

The fluorescence of single-colloidal CdSe quantum dots is investigated at r oom temperature by means of the autocorrelation function over a time scale of almost 12 orders of magnitude. Over a short time scale, the autocorrelat ion function shows complete antibunching, indicating single-photon emission and atomiclike behavior. Over longer time scales (up to tens of seconds), we measure a bunching effect that is due to fluorescence intermittency and that cannot be described by fluctuations between two states with constant r ates. The autocorrelation function also exhibits nonstationary behavior rel ated to power-law distributions of ON and OFF times. (C) 2001 Optical Socie ty of America.