Challenge to the Charging Model of Semiconductor-Nanocrystal Fluorescence Intermittency from Off-State Quantum Yields and Multiexciton Blinking

Abstract

Semiconductor nanocrystals emit light intermittently; i.e., they “blink,” under steady illumination. The dark periods have been widely assumed to be due to photoluminescence (PL) quenching by an Auger-like process involving a single additional charge present in the nanocrystal. Our results challenge this long-standing assumption. Close examination of exciton PL intensity time traces of single CdSe(CdZnS) core (shell) nanocrystals reveals that the dark state PL quantum yield can be 10 times less than the biexciton PL quantum yield. In addition, we observe spectrally resolved multiexciton emission and find that it also blinks with an on/off ratio greater than 10:1. These results directly contradict the predictions of the charging model.

Two-state theory of binned photon statistics for a large class of waiting time distributions and its application to quantum dot blinking

“…As an extension of this framework, multiply charged states were suggested in order to account for a dark-state quantum yield much lower than its biexcitonic counterpart. 29 Multiply charged states are also consistent with the distribution of lifetimes in the dark state 38 as well as the present findings on the distribution of dark intensity states. The wide distribution of bright intensity states reported in this paper could be due to an alternative mechanism of fluctuating non-radiative channels.…”

“…Unbiased estimations could be subtracted by considering the peaks within the intensity histogram rather than looking at counts from individual bins. 29 For example, the dark intensity fitted to the trajectory in Fig. 2 could be anywhere in the 0-4 counts/10 ms range, depending on background noise.…”

Magneto-optical properties of trions in non-blinking charged nanocrystals reveal an acoustic phonon bottleneck

“…Furthermore, we have shown that both trion charge states and concomitantly their charged biexcitons have high luminescence quantum yields, contrary to observations at room temperature 25 , indicating that Auger recombination is inefficient in these materials. Thus the photo-charging mechanism of our NCs can be attributed to a tunnelling process, which has significant implications for alternative photoluminescenceblinking mechanisms 41,42 . Another interesting consequence of NC engineering is revealed in the g-factor measurements.…”

Colloidal lead halide perovskite nanocrystals: synthesis, optical properties and applications

“…However, charging of NCs can promote Auger recombination and trap states can bind charge Colloidal lead halide perovskite nanocrystals H Huang et al carriers, preventing recombination, all of which has been considered to contribute to blinking. [102][103][104] Tian et al 98 observed PL blinking from MAPbI 3 nanorods (Figures 8h-j) and attributed it to photo-induced activation and de-activation of PL quenching sites, presumably present at the ends of the rods where formation of geometrical and chemical defects are most likely to occur. Similarly, blinking was also observed in single perovskite MAPbBr 3 NCs and attributed to the presence of charge trapping surface states.…”