September 16, 2025
Shown here is an electron micrograph of quantum dots encased in thick shells (white shapes) that were grown in UW Professor Brandi Cossairt’s lab. These quantum dots emit red light and are only about 4 nanometers in diameter. The thick shell brings the total diameter to 100 nanometers and makes the quantum dots easier to manipulate one at a time.Brandi Cossairt/University of Washington
Television technology has leveled up over the past few years. First there were high-definition TVs and now there are TVs with OLED and QLED screens. QLED TVs, which boast brighter colors over their OLED counterparts, use particles called “quantum dots” to generate their pixels.
Quantum dots, which are 10,000 times smaller than the width of a human hair, are unique materials that generate very specific colors of light. Researchers, including Brandi Cossairt, University of Washington professor of chemistry, hope that quantum dots can one day be useful for more than just illuminating screens.
Cossairt’s lab makes quantum dots for a variety of potential applications, including advanced computing. UW News asked her to compare the quantum dots in QLED TVs with the ones her lab makes.
Brandi Cossairt
So what exactly is a quantum dot?
Brandi Cossairt: It’s a material built from a lattice of atoms. Think about diamonds, which are made from a lattice of carbon atoms. If you take a diamond and you shrink it down to a very, very, very small scale to where there are only a few, maybe 100, carbon atoms — that’s kind of what a quantum dot looks like. Our quantum dots have the exact same structure as a diamond, except instead of carbon atoms, it contains other atoms, such as indium atoms and phosphorus atoms, or cadmium atoms and selenium atoms.
How do quantum dots generate light?
BC: Our quantum dots are semiconductors. This is a fundamental type of material that is defined as having an energy gap between where the electrons are and where they are not. This is different from a material like a metal, for example, where it’s easy for electrons to move around. In a semiconductor, the electrons and empty spots are very separated in terms of energy, and you need to apply energy to move electrons into empty spots. And once you’ve moved one, it’s “excited,” and it needs to “relax” back down to where it came from. One way that it does that is by releasing a photon, generating light.
Because quantum dots are so small, the color of light that they generate depends on their size. For example, larger quantum dots generate a red color and smaller quantum dots generate a blue color. This is different from a bulk semiconductor where the color of light is fixed, regardless of its size. So that’s kind of fun: By changing the size of the dot, you can change the color of light that is generated. That’s why we like them a lot.
What’s happening in a QLED TV?
BC: The way that current quantum dot TVs work is they shine a blue LED through a film containing a mixture of red- and green- emitting quantum dots. The quantum dots absorb that blue light, get excited, and then release red and green photons. Mixing that with blue from the LED is what generates the red, green and blue color pixels in the TV. You can precisely mix little bits of blue and green and red to get any color you want. That’s how you get all the colors the human eye can see.
What else do you want to use quantum dots for?
BC: The hope is that in the future we might be able to use light generated from quantum dots to do very large computations. Currently, we are limited in terms of the number of transistors we can pack onto a computer chip. Eventually, we’re going to reach some fundamental limit of how much information we can process with our chips.
People are trying to come up with new ways to get beyond the traditional way we do computing with zeros and ones. Photons are nice because they have quantum properties, such as the ability to exist in two different states at the same time, which allows us to use them to process much more information. We’re very far from that reality, but the idea is provocative and exciting. It’s an opportunity for scientists to think and dream and discover.
What’s getting in the way of making this a reality?
BC: In order to do something productive, you need to have many identical photons interacting, and that’s the hard part. You need all the photons that are generated to be exactly the same: exactly the same color and frequency and phase and all that stuff. And that’s really hard.
Right now, if we made 1,000 single quantum dots, they wouldn’t all give you exactly the same flavor of photon. They’d be close enough for a TV — that collection of quantum dots would give you a really nice red for example. But it’d still be a span of energies. It’s good enough for our eyeballs, but it’s not good enough for a quantum information system.
What are other challenges that you’re working on?
BC: So even if we did make quantum dots better at emitting pure, indistinguishable, single photons, we still need a way to put them onto a chip to do these computations. We need to position them exactly where we want them. It’s very hard to do. Recently we worked with our collaborator, Devin MacKenzie, UW associate professor of both mechanical engineering and materials science and engineering, to use inkjet printing to place quantum dots.
Here’s what we did: We took our quantum dot, which is really tiny — and it needs to be tiny to do all the fun, cool light emission stuff — and then we buried it into a big shell of some other material. Now we have something that’s 100 nanometers in diameter, instead of 3 nanometers in diameter. A 100-nanometer object is a bit easier to manipulate one particle at a time.
Then we made an ink containing these 100 nanometer particles, which we ejected through the nozzle of an inkjet printer using an electric field. This allowed us to strategically position these particles on photonic cavities, which is kind of like the building block for a photonic quantum computer. So that’s exciting.
This has been a really fun, collaborative project that also included a variety of researchers, such as Devin and Arka Majumdar, UW professor of electrical and computer engineering. My group was responsible for the synthesis of the quantum dots and putting them into their shells. This project has really gone far, and we’re excited to see what we can do with it next.
For more information, contact Cossairt, who is the Lloyd E. and Florence M. West Endowed Professor of Chemistry and a researcher with the UW Clean Energy Institute, at cossairt@uw.edu.
Tag(s): Brandi Cossairt • College of Arts & Sciences • Department of Chemistry • Research Makes America