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Television technology has advanced significantly in recent years. Initially, high-definition TVs were introduced, followed by screens featuring OLED and QLED technology. QLED TVs, which showcase more vibrant colors compared to their OLED alternatives, utilize substances known as “quantum dots” for pixel generation.

Quantum dots, measuring 10,000 times smaller than the width of a human hair, are extraordinary substances that produce distinctly specific colors of light. Scientists, including Brandi Cossairt, a chemistry professor at the University of Washington, have aspirations that quantum dots may one day serve purposes beyond merely illuminating screens.

Cossairt’s lab produces quantum dots for a range of potential uses, including advanced computing applications. UW News inquired about how the quantum dots in QLED TVs compare with those manufactured in her lab.

What precisely is a quantum dot?

Brandi Cossairt: It’s a substance formed from a lattice of atoms. Imagine diamonds: they’re constructed from a lattice of carbon atoms. If you were to minimize a diamond to a very, very, very small size, potentially containing only a few, maybe 100, carbon atoms — that’s somewhat analogous to what a quantum dot resembles. Our quantum dots possess the identical structure of a diamond, but instead of carbon atoms, they consist of different atoms such as indium and phosphorus or cadmium and selenium.

How do quantum dots emit light?

BC: Our quantum dots function as semiconductors. This fundamental type of material is characterized by an energy gap between the regions where electrons are present and where they are absent. This contrasts with materials like metals, where electrons can move easily. In a semiconductor, the electrons and vacant spaces are significantly separated in terms of energy, requiring energy application to displace electrons into these vacant areas. Once one is moved, it becomes “excited” and must “relax” back to its original state. One method of doing this is by emitting a photon, thereby producing light.

Because quantum dots are so minuscule, the hue of light they produce is contingent on their size. For instance, larger quantumdots emit red light, while smaller ones generate blue light. This contrasts with bulk semiconductors, where the emitted light’s color remains constant regardless of size. This variability is intriguing: altering the dot’s size allows for changes in the emitted light color. This is precisely why we find them so appealing.

What occurs within a QLED TV?

BC: The operation of contemporary quantum dot TVs involves projecting blue LED light through a film containing a blend of quantum dots that emit red and green light. The quantum dots absorb the blue light, become excited, and subsequently release red and green photons. This blending with blue from the LED results in the red, green, and blue color pixels displayed on the TV. You can carefully mix small amounts of blue, green, and red to achieve any color desired. This is how all the colors visible to the human eye are produced.

What additional applications do you envision for quantum dots?

BC: The aspiration is that, in the future, we could leverage light produced from quantum dots for extensive computations. Currently, we’re constrained by the number of transistors we can incorporate into a computer chip. Eventually, we will encounter a fundamental limit on the amount of information we can process using our chips.

Researchers are exploring innovative methods to transcend the traditional binary computing approach. Photons are advantageous because they possess quantum characteristics, such as the ability to exist in two different states simultaneously, allowing for the processing of significantly more information. While we are quite distant from achieving this reality, the concept is both intriguing and exhilarating. It offers scientists a chance to think, dream, and innovate.

What obstacles stand in the way of bringing this vision to fruition?

BC: To achieve something productive, a multitude of identical photons must interact, and this is the challenging aspect. All generated photons must be precisely the same: identical in color, frequency, phase, and all those characteristics. Achieving this uniformity is quite arduous.

As it stands, if we were to create 1,000 individual quantum dots, they wouldn’t all emit exactly the same type of photon. They would be sufficiently close for television purposes; that assortment of quantum dots might produce a very nice red, for instance. However, there would still be a range of energies involved. It’s adequate for our eyes, but not suitable for a quantum information system.

What other challenges are you addressing?

BC: Even if we manage to enhance quantum dots for the emission of pure, indistinguishable, single photons, we still require a method to position them on a chip for computational purposes. Precise placement is crucial, and it’s quite challenging to accomplish. Recently, we collaborated with our associate, Devin MacKenzie, assistant professor of mechanical engineering and materials science and engineering at UW, to utilize inkjet printing for quantum dot placement.

Here’s what we did: We took our quantum dot, which is incredibly tiny — and it needs to be small to facilitate all the exciting light emissions — and we encapsulated it in a larger shell of another substance. This transformed it into a 100-nanometer particle, rather than a 3-nanometer one. A 100-nanometer object is considerably easier to manipulate individually.

Subsequently, we created an ink incorporating these 100-nanometer particles, which we propelled through the nozzle of an inkjet printer using an electric field. This approach allowed us to strategically place these particles on photonic cavities, akin to foundational elements for a photonic quantum computer. This is truly exciting.

This process has been a remarkable experience,

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A joint endeavor that encompassed a diverse group of scientists, including Devin and Arka Majumdar, a professor at UW specializing in both physics and electrical and computer engineering. My team was tasked with the creation of quantum dots and enclosing them within their shells. This initiative has indeed progressed significantly, and we’re eager to explore what we can achieve moving forward.

For additional details, reach out to Cossairt, who serves as the Lloyd E. and Florence M. West Endowed Professor of Chemistry and is affiliated with the UW Clean Energy Institute, at [email protected].

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