The 2014
Nobel Prize for physics has been awarded to a trio of scientists in Japan and
the US for the invention of blue light emitting diodes (LEDs). Professors Isamu
Akasaki, Hiroshi Amano and Shuji Nakamura made the first blue LEDs in the early
1990s. This enabled a new generation of bright, energy-efficient white lamps,
as well as colour LED screens.
The winners
will share prize money of eight million kronor (£0.7m).
Making the
announcement, the Nobel jury emphasized the usefulness of the invention, adding
that the Nobel Prizes were established to recognize developments that delivered
"the greatest benefit to mankind.
Albeit red
and green LEDs had been around for a long time, blue LEDs were a long-standing
test for researchers in both the scholarly world and industry. Without them,
the three colors couldn't be blended to deliver the white light we now see in
LED-based machine and TV screens. Moreover, the high-vitality blue light could
be utilized to energize phosphorus and straightforwardly deliver white light -
the premise of the up and coming era of light.
Working
The LED
consists of a chip of semiconducting material doped with impurities to create a
p-n junction. As in other diodes, current flows easily from the p-side, or
anode, to the n-side, or cathode, but not in the reverse direction.
Charge-carriers—electrons and holes—flow into the junction from electrodes with
different voltages. When an electron meets a hole, it falls into a lower energy
level and releases energy in the form of a photon. The wavelength of the light
emitted, and thus its color, depends on the band gap energy of the materials
forming the p-n junction. In silicon or germanium diodes, the electrons and
holes usually recombine by a non-radiative transition, which produces no
optical emission, because these are indirect band gap materials. The materials
used for the LED have a direct band gap with energies corresponding to
near-infrared, visible, or near-ultraviolet light.
Why blue in particular?
Well, blue
was the last -- and most difficult -- advance required to create white LED
light. And with white LED light, companies are able to create smartphones and computer screens, as well as light bulbs
that last longer and use less electricity than any bulb invented before.
LEDs are
basically semiconductors that have been built so they emit light when they're
activated. Different chemicals give different LEDs their colors. Engineers made
the first LEDs in the 1950s and 60s. Early iterations included laser-emitting
devices that worked only when bathed in liquid nitrogen. At the time,
scientists developed LEDs that emitted everything from infrared light to green light…
but they couldn't quite get to blue. That required chemicals, including
carefully-created crystals, that they weren't yet able to make in the lab.
