The Grand Discovery of Quantum Dots: An Overview

Sunday - October 29 2023, 11:01 UTC - 1 year ago

Discovering quantum dots in 1980s was an accident, as it was observed that the colors of the semiconductor particles changed when lasers were pointed at them. Quantum dots are smaller than wavelength of light and are now being used in LED lighting, medical diagnostics and displays.

When you were working at Bell Labs in the 1980s and discovered quantum dots, it was something of an accident. You were studying solutions of semiconductor particles. And when you aimed lasers at these solutions, called colloids, you noticed that the colors they emitted were not constant.

On the first day we made the colloid, sometimes the spectrum was different. Second and third day, it was normal. There certainly was a surprise when I first saw this change in the spectrum. And so, I began to try to figure out what the heck was going on with that.

I noticed that the property of the particle itself began to change at a very small size.

What you’d found was a quantum dot: a type of nanoparticle that absorbs light and emits it at another wavelength. Crucially, the color of these particles changes depending on the actual size of the particle. How do you even see a quantum dot crystal, since one is just a few hundred thousandths the width of a human hair? .

Well, you can’t see them with an optical microscope because they’re smaller than the wavelength of light. There are ways to see them too, using other types of specialist microscopes, such as an electron microscope. And a common way of demonstrating them is to line up a row of brightly colored glass flasks each with a solution of different sized quantum dots inside it.

One of your fellow laureates, Alexei Ekimov, was a Russian scientist, and he’d actually observed quantum dots in colored glass, but you weren’t aware of his findings at the time? .

Yes, that’s right. The Cold War was going on at that time, and he published in the Russian literature, in Russian. And he wasn’t allowed to travel to the West to talk about his work.

I asked around among all the physicists, was there any work on small particles? I was trying to make a model of the quantum size effects. And they told me no, nobody’s really working on this. Nobody had seen his articles, basically.

I was part of the U.S. chemistry community, doing synthetic chemistry in the laboratory. He was in the glass industry in the Soviet Union, working on industrial technology.

When I eventually found his articles in the technological literature, I wrote a letter to the Soviet Union, with my papers, just to say hello to Ekimov and his colleagues. When the letter came, the KGB came to talk to the Russian scientists, trying to figure out why they had any contact with anybody in the West. But in fact they had never talked to me or anyone in the West when my letter arrived in the mail.

Have you met him since? .

Yes, they were able to come out of the Soviet Union during Glasnost, this would be the late 1980s. There’s Ekimov, and then there is his theoretical collaborator Sasha Efros, who now works at the U.S. Naval Research Lab. I met them as soon as they came to the U.S.

One of the issues with quantum dots, when you first observed them, was how to actually produce them and keep them stable. Then, in the 1990s, your fellow laureate, Moungi Bawendi, figured this out. What do you think is the most striking thing that you’ve seen quantum dots used in so far? .

Usually when a new material is invented, it takes a long time to learn all the different possible applications. But in this case, it went very quickly. Initially, the idea was for semiconductor lasers, but now quantum dots are being used in almost everything, from LED lighting to medical diagnostics. But most of what I’ve done has been in displays.