Blinking statistics correlated with nanoparticle number.

We report fluorescence of single semiconductor nanorods (NRs) and few-NR clusters, correlated with transmission electron microscopy for direct determination of the number of NRs present in a single fluorescent source. For samples drop-cast from dilute solutions, we show that the majority of the blinking sources (approximately 75%) are individual NRs while the remaining sources are small clusters consisting of up to 15 NRs. Clusters containing two or three NRs exhibit intermittent fluorescence intensity trajectories, I(t), similar to those of individual NRs. The associated statistical parameters of on- and off-time probability densities for two- and three-NR clusters are indistinguishable from those of individual NRs. In contrast, statistically distinguishable blinking parameters are observed for clusters of five or more particles. In particular, the "truncation time" of the on-time probability density, i.e., the time characterizing the transition from a power law to an exponential decay, was found to increase superlinearly with the number of particles. Our long (2.4 x 10(4) s) blinking measurements also directly reveal the previously unobserved truncation of the power law distribution of the off-times for single nanoparticles.