The blue LED was a milestone development, but now the race is on to manufacture the next leap in lighting technology.
Producing blue, green and red light-emitting diodes from the same set of materials will mean being able to make integrated LEDs on the same substrate. This would allow components to be miniaturized, opening the door to an array of new applications, from ultra-small projectors to multi-color lighting sources.
Although blue and green LED elements are made using gallium nitride crystals, red LEDs use a different material that combines gallium, indium and phosphorous. But recent studies show that red light can also be tweaked from gallium nitride by adding the rare earth material europium. Having all three LED colors on the same base would allow a single source to power them all.
Primary colors
This research is being conducted by Yasufumi Fujiwara and others from Osaka University, together with colleagues from the University of Amsterdam and Lehigh University in the U.S. Working together, these scientists are investigating how to convert electricity into more efficient light energy. In the process, they discovered a mechanism for generating red light from gallium nitride. Over the next two years, they expect this method to generate red light that can match the intensity of the LEDs now in use.
Meanwhile, a group at Sophia University led by Katsumi Kishino has developed a new LED structure that resembles a tiny bed of nails. Each "nail" is tens to hundreds of nanometers thick. The nail-like rods are made from a semiconductor compound of gallium nitride mixed with indium. Adjusting the indium content and the thickness of the nails causes the color of the emitted light to change.
So far, Kishino's team has managed to create blue, green, orange and yellowish light this way, but they believe other colors can also be generated using the same principle. Their goal is to have a wide range of colors ready within five years.
Researchers at the University of Tokyo, led by professor Hiroshi Fujioka, have also succeeded in generating the three primary colors using LEDs on a single substrate. They grow gallium nitride crystals on a thin sheet of carbon monocule in the form of graphene, which is spread over an inexpensive glass substrate. Adding different amounts of indium to the gallium nitride changes the color emitted.
Blue light was long the holy grail of LED research, and led to the explosive growth of LEDs and a Nobel Prize for its developers. The light emitting diodes are now a ubiquitous feature of daily technology and are essential components for a wide variety of products, from flat-panel televisions and tablets to room lighting and traffic signals.
Future possibilities
But blue, red and green LED elements are currently handled as separate components, so the potential for new developments will rise sharply once all three colors can be emitted using the same material.
If realized, one possibility is a miniature projector small enough to fit inside a pen or a smartphone. A device of this nature could project movies even in bright light conditions. Since LEDs are bright and consume relatively little power, this kind of projector could be battery powered.
The new light intensive, energy efficient diodes could also be used for high-resolution screens in glasses. With displays in each lens presenting a slightly different image for the left and right eyes, 3-D movies could also be possible.
Full-color room illumination is another possibility. Today's white LEDs are made by coating blue LEDs with yellow phosphor materials, which sacrifices a little brightness. If white light were generated from LEDs without this coating, then the lights would be brighter and save energy.
Materials are also stimulating scientific creativity. Gallium nitride's use in semiconductors for computing and communications has inspired professor Fujioka to study the possibility of developing a device in the form of a single thin sheet that can switch between uses as a television, phone and computer.