Color by Size: Quantum Dots

Why do we see green leaves and red fire trucks? When we look at most objects, they appear

color

ed because radiation from the Sun bounces off them in light waves called photons. Photons scatter from objects and are received by our eyes. But when you watch television, where do the

color

s come from? Today, the colors on most television screens come from a series of small lamps called light-emitting diodes, or LEDs. These LEDs emit three basic colors: red, green and blue. To create other colors, LEDs combine these three colors in various proportions. Since LEDs emit three colors with broad color profiles, they can have difficulty representing colors with high accuracy.

Quantum

dots

, on the other hand, are a new technology capable of emitting colors with much more precision. Scientists hope to fine-tune the distribution of colors so that blue becomes bluer, green becomes greener, and red becomes redder! Quantum

dots

are microscopic: the

size

of a

quantum

dot relative to a human is like the

size

of a human relative to the Sun! They are made from materials called semiconductors that have special properties. Semiconductors have energy bands between which electrons can move. When a photon collides with an electron, the electron absorbs the photon's energy and jumps to a higher energy band.

To relax to a lower energy band, the electron can release a photon that matches the energy difference. This means that the difference between the two energy levels determines the energy of the released photon, which is related to the color of the light. Scientists can alter the size of

quantum

dots to adjust the energy difference between the two bands and change the color of the light emitted by the dot. Smaller dots actually have a larger energy difference between the energy bands. To return to the lower energy band, electrons must emit a photon with high energy, creating colors with short wavelengths, such as blue or violet.

Larger spots have smaller energy differences between bands. These large dots emit lower energy light with longer wavelengths, creating yellow or red hues. Scientists have been working hard to create quantum dots with high efficiency. For each photon absorbed by these quantum dots, several photons of the specific color of the quantum dot come out. Many newer televisions today use quantum dots because they produce purer colors in a more energy-efficient way than the LEDs used in conventional televisions. However, quantum dots could be used in much more than just television screens! With more accurate colors, astronomers could collect more precise data on the spectra of light coming from distant stars, giving more accurate readings of the object's age and composition.

Additionally, quantum dots can be used to capture sunlight and convert it into electricity. Scientists are also using quantum dots to develop better medical imaging methods. Quantum dots could improve current technology of using dyes or other imaging agents to visualize cancerous tumors by providing better delineation between cancerous tissues and other tissues. Surgeons could operate with greater precision, helping to preserve the patient's healthy tissue. However, more research needs to be done to determine whether quantum dots are safe for use in humans. An advantage of using quantum dots is their small size, which allows them to be dispersed in liquids.

Therefore, many liquid processing techniques, such as inkjet printing and spin-coating, can be applied when using quantum dots. This allows quantum dots to be integrated into products quickly, easily and at low cost. Quantum dots are a new microscopic technology for emitting colored light. These little lights excite scientists because they are designed to emit very specific colors in a very efficient way, paving the way for more vivid and realistic displays. In the near future, there is a good chance that your mobile phone screen will be made of quantum dots! Soon quantum dot technology will color our lives!