intensity dependence of the ‘off’ state lifetimes, and discover that under strong excitation Auger processes do dominate the nonradiative decay. Finally, we present a phenomenologi- cal model accounting for the results, provide guidelines for the design of non-blinking QDs, and discuss possible experimental pathways to further elucidate the detailed dynamics of this fundamental system. CdSe/CdS/ZnS QDs were synthesized in three sizes following standard procedures [19]. Briefly, QDs were grown in a non-coordinating solvent and overcoated using successive ion layering [20]. We used nanocrystals with diameters of 3.8nm, 5nm and 8nm (corresponding to emission peaks at 590nm, 618nm and 665nm, respectively). All QDs were slightly rodlike, with an aspect ratio of ≈ 2. The quantum yield of the respective samples was determined in solution to be 80%, 70% and 15%. Nanomolar concentrations of QDs in a 3% mass/volume PMMA solution were spin-cast onto glass cover slips creating samples with typical densities of 0.02 QDs/ µm $^{2}$. The QDs were excited by frequency-doubled pulses from a Ti-Sapphire oscillator at 400nm, with a duration of 100fs and a repetition rate of 80MHz. Light was focused on the sample by an oil immersion objective with a numerical aperture of 1 . 4. Epi- fluorescence was spectrally filtered and detected by a single-photon avalanche photodiode (id Quantique). Emission time traces from isolated QDs were recorded by a time-correlated single photon counting system (Picoharp300, Picoquant), operated in the time-tagged mode such that each photon is assigned an absolute arrival time and an arrival time relative to the excitation pulse. The system temporal resolution was measured to be 65ps. A representative intensity histogram of a blinking QD is shown in Fig. 1(a). For each such data set we define the ‘on’ and ‘off’ count rate thresholds. ‘On’ and ‘off’ photoluminescence (PL) decay curves were produced by binning all photons which arrived during the respective periods according to their time of arrival relative to the excitation pulse. Both are presented in Fig. 1(b). For most observed QDs the ‘on’ state exhibits single exponential decay, in agreement with previous observations [17]. The ‘off’ state, however, demonstrates a more complicated decay curve with a wide range of lifetimes. Typical ‘off’ time decay curves con- tain both rapid components of ∼ 100ps and relatively long ones of ∼ 1ns. Multiexponential decays were previously observed on CdSe/ZnS QDs [17], and recently in CdSe/CdS QDs [8], implying that such behavior is is not unique to our system. Such measurements were performed on several tens of nanocrystals at each of the three sizes. As we cannot directly assign a lifetime to the ‘off’ state decay, we resort to assigning a 4