Observation of Correlated Emission Intensity and Polarization Fluctuations in Single CdSe/ZnS Quantum Dots

Abstract

Time-resolved single-nanoparticle spectroscopy has been carried out to examine the luminescence characteristics of individual CdSe/ZnS core/shell quantum dots. In particular, the possible correlations between emission intensity, lifetime, spectrum, and polarization fluctuations have been investigated. The emission polarization was found to be correlated with the luminescence intensity in a nonlinear way. The low-emissive states were found to correlate with red-shifted spectrum, increased nonradiative decay, and low degree of emission polarization. The observations are consistent with the model that charged quantum dots can be emissive.

Photoluminescence Intermittency from Single Quantum Dots to Organic Molecules: Emerging Themes

“…The giant QDs also exhibited clear “gray” or low-emissive states that lie between the highest intensity state and complete extinction (Figure 2) [50,52]. Evidence for multiple emissive states had also been reported for CdSe/ZnS [53], where low-emissive states were found to correspond to lower-energy emission and shorter lifetimes [54]. Although these gray states are short lived in ZnS capped QDs and require statistical rigor to detect, they are prolonged and visually evident in giant CdSe/CdS QDs allowing for detailed investigations of low quantum yield (QY) states and their role in PI.…”

Shell and ligand-dependent blinking of CdSe-based core/shell nanocrystals

“…In recent years, pulsed laser experiments showed the correlation of emission intensity, lifetime and polarization fluctuations in single nanocrystal blinking, suggesting time-dependent charge migration and fluctuation in nonradiative relaxation pathways. [46][47][48] Although the present model properly describes the shell-and ligand-dependent exciton blinking of nanocrystals under cw laser irradiation, further study is underway to take those ultrafast phenomena involving biexciton 49 and trion 37,50,51 into account.…”

Using the Near-Field Coupling of a Sharp Tip to Tune Fluorescence-Emission Fluctuations during Quantum-Dot Blinking

“…1(b). Single-photon counting experiments have revealed a correlation between a decrease in emission intensity and a decrease in the fluorescence lifetime [22][23][24][25], leading to the conclusion that a single QD can have many different internal states [24]. These studies in combination with extinction coefficient measurements showing similar absorption cross sections for low and high emissive states [26] suggest that the emission fluctuations are due to variations in q 0 corresponding to a relatively large number ($ 10) of states.…”