Soon, smartphones to have multi-functional displays

Cell phones and other devices could soon be controlled with touch-less gestures and charge themselves using ambient light, thanks to new LED arrays developed by scientists that can both emit and detect light.
Made of tiny nanorods arrayed in a thin film, the LEDs could enable new interactive functions and multitasking devices, researchers said.
"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 Moonsub Shim, professor at the University of Illinois at Urbana-Champaign in the US.
"That can become the basis for new and interesting designs for a lot of electronics," said Shim.

The tiny nanorods, each measuring less than five nanometres 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.

The nanorod LEDs 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 - in fact, it is three orders of magnitude faster than standard display refresh rates.

Yet 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.
Researchers demonstrated pixels that automatically adjust brightness, as well as pixels that respond to an approaching finger, which could be integrated into interactive displays that respond to touchless gestures or recognise objects.
They also demonstrated 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 found that the LEDs not only respond to light, but can convert it to electricity as well.
"The way it responds to light is like a solar cell. So not only can we enhance interaction between users and devices or displays, now we can actually use the displays to harvest light," Shim said.
In addition to interacting with users and their environment, nanorod LED displays can interact with each other as large parallel communication arrays.
It would be slower than device-to-device technologies like Bluetooth, Shim said, but those technologies are serial - they can only send one bit at a time.

Two LED arrays facing each other could communicate with as many bits as there are pixels in the screen.
The study was published in the journal Science.