Controlling the Blinking of Quantum Dots

A team led by ISN-affiliated MIT professors Keith Nelson, Moungi Bawendi, and Adam Willard has succeeded in controlling a decades old problem that plagues luminescent quantum dots (QDs) and has caused significant issues with their use in precision applications. The problem — the heretofore unavoidable tendency for QDs to blink off at random intervals — has been prevent by firing an infrared laser at the dots for just a few picoseconds, which has the effect of stopping the blinking for comparatively long periods of time, tens of billions of times longer than the pulse. Ultimately, this advance may lead to the more widespread adoption of quantum dots in such fields as quantum sciences and biomedical research.
A yellow light illuminates a cluster of spheres, representing quantum dots, showcasing MIT chemists' innovative control method.

MIT chemists have come up with a way to control the unwanted blinking of quantum dots, depicted here as yellow spheres, without requiring any modification to the formulation or the manufacturing process. Image courtesy of the researchers.

Schematic illustration of light sources and types, featuring CdSe/CdS QD with MIR pulse excitation and PL measurement techniques.

a, Schematic illustration of a single CdSe/CdS QD with MIR pulse excitation and various PL probes, including PL intensity, PL spectrum and (with pulsed rather than CW photoexcitation) time-resolved (TR) PL lifetime measurements. BPF, bandpass filter. b, In the conventional charging model for PL blinking, ON and OFF periods correspond to a neutral nanocrystal (exciton) and a charged nanocrystal (trion), respectively. During the OFF periods, ultrafast MIR fields can effectively remove the excess charge in a trion and convert it to an exciton. c, The spectrum of MIR pulses is centred at ~5.5 μm with a bandwidth of ~0.5 μm. a.u., arbitrary unit. d, The second-order PL intensity correlation function g2(t) measured at time zero t = 0 for a single QD indicates that g2(0) = 0.1. Image: Shi, J., Sun, W., Utzat, H. et al. All-optical fluorescence blinking control in quantum dots with ultrafast mid-infrared pulses. Nat. Nanotechnol. 16, 1355–1361 (2021).