Why do we see leaves as green and fire
trucks as red? When we look at most
objects, they appear colored because
radiation from the Sun bounces off them
in light waves called photons. Photons
scatter off objects and are received by
our eyes. But when you watch TV, where do
the colors come from? Today, colors on
most TV screens come from a series of
tiny lamps called light-emitting diodes
or LEDs.
These LEDs emit three basic colors: red
green, and blue. In order to make other
colors, the LEDs combine these three
colors in various proportions.
Since LEDs emit three colors with broad
color profiles, they can struggle to
represent colors with high-precision.
Quantum dots, on the other hand, are a new
technology capable of emitting colors
much more accurately. Scientists hope to
fine tune the distribution of colors so
that the blue becomes bluer, the green
becomes greener and the 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 which
have special properties.
Semiconductors have energy bands that
electrons can move between. When a photon
hits 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 the difference between the two
energy levels determines the energy of
the photon released, which is related to
the color of the light. Scientists can
alter the size of the quantum dots to
fine-tune 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 energy bands. To get
all the way back down to the lower
energy band, electrons must emit a photon
with high energy, creating colors with
short wavelengths, like blue or violet.
Larger dots have smaller energy
differences between bands. These large
dots give off a lower energy light with
longer wavelengths, creating hues of
yellow or red. Scientists have been
working hard to create quantum dots with
high efficiency. For every photon these
quantum dots absorb, several photons of
the quantum dot's specific color come
back out. Many newer TVs today use
quantum dots because they
produce more pure color in a more
energy-efficient way than LEDs used in
conventional TVs. However, quantum dots
could be used in much more than just TV
screens! With more precise colors,
astronomers could collect more accurate
data about the spectra of light coming
from distant stars, giving more exact
readings of the object's age and
composition. In addition, quantum dots can
be used to harvest sunlight and convert
it into electricity. Scientists are also
using quantum dots to develop better
methods of medical imaging. Quantum dots
could improve on the current technology of
using dyes or other imaging agents to
visualize cancer tumors by providing a
better delineation between cancerous
tissues and other tissues. Surgeons could
operate with greater precision, helping
preserve a patient's healthy tissue.
However, more research needs to be done
to determine if quantum dots are safe to
use in humans. One advantage of using
quantum dots as 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 a low cost. Quantum dots
are a new microscopic technology for
emitting colored light. These tiny lights
excite scientists because they are
designed to emit highly specific colors
in a very efficient way paving the way,
paving the way for more vivid, lifelike displays. In the
near future, there's a good chance your
cellphone screen could be made from
quantum dots! Soon quantum dot technology
will color our lives!