By David L. Chandler, Massachusetts Institute of Technology
November 26, 2021
The new technique is described in a paper released on November 22, 2021, in the journal Nature Nanotechnology, by doctoral trainees Jiaojian Shi, Weiwei Sun, and Hendrik Utzat, teachers of chemistry Keith Nelson and Moungi Bawendi, and five others at MIT.
Quantum dots are tiny particles, just a couple of nanometers across, made of semiconductor material, which has a “bandgap” between the energy levels of its electrons. When such materials gain energy from light shining on them, electrons can leap to a greater energy band; when they revert to their previous level, energy is released in the form of a photon, a particle of light. The frequency of this light, which determines its color, can be exactly tuned by selecting the shapes and dimensions of the dots. Besides screen screens, quantum dots have possible for usages as solar batteries, transistors, lasers, and quantum info devices.
The blinking phenomenon was first observed in the 1990s, soon after quantum dots were initially made. A lot of effort went into attempting to eliminate it by crafting the interface between the dot and its environment, or by adding other molecules. None of these things actually worked well or were very reproducible.”
” We know that for some quantum info applications, we want a perfect single-photon emitter source,” Sun explains. With presently offered quantum dots, which otherwise may be well-suited to such applications, “they will turn on off arbitrarily, and this is actually damaging for any of the applications that make use of the photoluminescence from the dots.”
Now, she says, thanks to the teams research, “we use these ultra-fast mid-infrared pulses, and the quantum dots can stay in the on state. This can possibly be really helpful for applications, like in quantum info science, where you truly need an intense source of single photons without any intermittency.”
For biomedical research applications, getting rid of the blinking is important, Shi states. This could lead to more effective drug-discovery procedures, he says, “but if the quantum dots start blinking a lot, you basically lose track of where the particle is.”
Nelson, who is the Haslam and Dewey Professor of Chemistry, explains that the reason for the blinking phenomenon most likely pertains to extra electrical charges, such as additional electrons, connecting to the outer part of the quantum dots, changing the surface residential or commercial properties so that there are other alternative paths for the additional energy to be released rather of by producing light.
” Various things can occur in a genuine environment,” Nelson states, “such that possibly the quantum dot has an electron glommed onto it somewhere at the surface area.” Rather of being electrically neutral, the quantum dot now has a net charge, and while it can still return to its ground state by discharging a photon, “the extra charge sadly also opens up an entire bunch of additional pathways for the electrons excited state to return to the ground state without producing a photon,” for instance by shedding heat instead.
However when zapped with a burst of mid-infrared light, the extra charges tend to get knocked off the surface area, enabling the quantum dots to produce steady emissions and stop their blinking.
It turns out, Utzat says, that this is “an extremely general procedure,” which might end up being helpful for handling anomalous intermittency in some other gadgets, such as in so-called nitrogen job centers in diamond, which are being utilized for ultra-high-resolution microscopy and as sources of single-photons in optical quantum technologies. “Even though we have actually shown it for just one type of workhorse material, the quantum dot, I think that we can use this technique to other emitters,” he says. “I believe the fundamental result of utilizing this mid-infrared light is applicable to a wide variety of different materials.”
Nelson states the impact also might not be limited to the mid-infrared pulses, which currently rely on bulky and costly lab laser devices and are not yet all set for commercial applications. The same principle might likewise reach terahertz frequencies, he says, an area that has been under advancement in his laboratory and others and that in concept might result in much smaller sized and less costly gadgets.
Recommendation: “All-optical fluorescence blinking control in quantum dots with ultrafast mid-infrared pulses” by Jiaojian Shi, Weiwei Sun, Hendrik Utzat, Ardavan Farahvash, Frank Y. Gao, Zhuquan Zhang, Ulugbek Barotov, Adam P. Willard, Keith A. Nelson and Moungi G. Bawendi, 22 November 2021, Nature Nanotechnology.DOI: 10.1038/ s41565-021-01016-w.
The research group likewise included Ardavan Farahvash, Frank Gao, Zhuquan Zhang, Ulugbek Barotov, and Adam Willard, all at MIT. The work was supported by the U.S. Army Research Lab and the U.S. Army Research Office through the Institute for Soldier Nanotechnologies, the U.S. Department of Energy, and the Samsung Global Outreach Program.
Quantum dots, found in the 1990s, have a wide range of applications and are perhaps best understood for producing brilliant colors in some high-end televisions. Quantum dots are small particles, simply a few nanometers across, made of semiconductor material, which has a “bandgap” between the energy levels of its electrons. Display screen screens, quantum dots have potential for uses as solar cells, transistors, lasers, and quantum info devices.
The blinking phenomenon was first observed in the 1990s, soon after quantum dots were initially made. “Even though we have actually revealed it for just one kind of workhorse material, the quantum dot, I believe that we can use this method to other emitters,” he says.
MIT chemists have developed a way to control the unwanted blinking of quantum dots, illustrated here as yellow spheres, without requiring any modification to the solution or the manufacturing process. Credit: Courtesy of the scientists
New technique solves a relentless issue of intermittency that has actually prevented use of the small light emitters for biological imaging or quantum photonics.
Quantum dots, discovered in the 1990s, have a vast array of applications and are maybe best known for producing vibrant colors in some high-end tvs. But for some prospective uses, such as tracking biochemical paths of a drug as it connects with living cells, progress has actually been obstructed by one apparently unmanageable quality: a propensity to blink off at random periods. That doesnt matter when the dots are utilized in the aggregate, as in television screens, but for precision applications it can be a substantial downside.
Now, a team of chemists at MIT has actually developed a method to control this undesirable blinking without needing any modification to the formulation or the manufacturing process. By shooting a beam of mid-infrared laser light for an infinitesimal moment– a few trillionths of a second– the quantum dots blinking is removed for a reasonably extended period, 10s of billions of times longer than the laser pulse.
