Core Concept: Quantum dots.

In September 2015, Philips, an electronics company based in The Netherlands, unveiled a computer monitor that achieved a brilliant color display using quantum dots: semiconductor nanocrystals that can be tuned to glow in any color. The Philips monitor was the first of its kind, following on the heels of the television that uses quantum dots to enhance its backlighting—rolled out by Sony in 2013—and arriving a few months before the anticipated rollout of the first quantum dot-driven smartphone camera sensors, which the company InVisage announced would start appearing in phones in 2016. These screens have the same resolution as high-definition but can reportedly display a wider range of colors—and potentially at a lower cost—than existing devices. The term “quantum dots,” it seems, has gonemainstream. First identified 35 years ago (1), quantum dots have been evolving in the clean laboratories of curious physicists and engineers, out of sight of the general public, a revolutionary idea without a breakthrough application. They’re tiny crystals, grown from or etched into semiconductor materials, with diameters ranging from one nanometer to a few dozen nanometers—on the order of a small virus. When excited by electricity or light, a quantum dot produces a brilliant, singlecolor glow. Quantum dots occupy a sweet spot in the semiconductor size spectrum. They typically contain relatively few atoms, ranging from about 1,000 to 100,000. That means the crystals are large enough to be useful in the laboratory, but so small that they exhibit quantum behaviors associated with individual atoms. They’re a classic example of “artificial atoms”: semiconductor particles sufficiently tiny such that charge and energy levels are quantized.Movement of electrons is confined in all three directions so tightly that quantum dots are said to be “zero-dimensional.”As a result, changing the size of a quantum dot controls how it absorbs and emits energy. This behavior makes them appealing for a wide range of photonics and electronics applications. Some researchers think quantum dots will boost efficiency in LEDs and solar cells, or be used to create glowing paint. Others see potential for using quantum dots as quantum bits or “qubits” to store data in a quantum computer. Quantum bits also may be used as singlephoton emitters, devices that would allow for the creation of quantum communication networks based on sending light signals from node to node (2). Their potential extends to other fields: biologists are using the fluorescence of quantum dots to tag cells of interest within a larger sample, an imaging technique that could be particularly useful in molecular cancer research by easily highlighting tumor cells or receptors on cells (3).