New LED arrays that can both emit and detect light could open the door for mobile phones and other devices that could be controlled with touchless gestures and charge themselves using ambient light.
Researchers from the University of Illinois at Urbana-Champaign and Dow Electronic Materials have developed the LEDs which are made of tiny nanorods arrayed in a thin film.
These nanorods, each measuring less than 5 nm in diameter, are made of three types of semiconductor material.
One type emits and absorbs visible light. The other two semiconductors control how charge flows through the first material. The combination is what allows the LEDs to emit, sense and respond to light.
They are able to perform both functions by quickly switching back and forth from emitting to detecting. They switch so fast that, to the human eye, the display appears to stay on continuously. But the LEDs are also near-continuously detecting and absorbing light, and a display made of the LEDs can be programmed to respond to light signals in a number of ways.
For example, a display could automatically adjust brightness in response to ambient light conditions – on a pixel-by-pixel basis.
“You can imagine sitting outside with your tablet, reading. Your tablet will detect the brightness and adjust it for individual pixels,” said UI Professor Moonsub Shim.
“Where there’s a shadow falling across the screen it will be dimmer, and where it’s in the sun it will be brighter, so you can maintain steady contrast.”
The team demonstrated pixels that automatically adjust brightness, pixels that respond to an approaching finger, which could be integrated into interactive displays that respond to touchless gestures or recognise objects, and arrays that respond to a laser stylus, which could be the basis of smart whiteboards, tablets or other surfaces for writing or drawing with light.
The researchers also found that the LEDs not only respond to light, but can convert it to electricity as well.
“These LEDs are the beginning of enabling displays to do something completely different, moving well beyond just displaying information to be much more interactive devices,” said UI Professor Moonsub Shim. “That can become the basis for new and interesting designs for a lot of electronics.”
[A laser stylus writes on a small array of multifunction pixels made by dual-function LEDs that can both emit and respond to light. Photo: Moonsub Shim/UI]