Spontaneous Spectral Diffusion in CdSe Quantum Dots

Spectral diffusion of the emission line of single colloidal nanocrystals is generally regarded as a random process. Here, we show that each new spectral position has a finite memory of previous spectral positions, as evidenced by persistent anticorrelations in time series of spectral jumps. The anticorrelation indicates that there is an enhanced probability of the charge distribution around the nanocrystal returning to a previous configuration. We show both statistically and directly that this memory manifests as an observable spontaneous relaxation in the absence of a pump laser, so that spectral diffusion progresses in a manner of two steps forward and one step back.