Dual Function LEDs & Multifunctional Displays

At the University of Illinois at Urbana-Champaign, researchers have made dual-function nanorod LEDs that could double as multifunctional displays. The researchers are also working with Dow Electronic Materials in Marlborough, Massachusetts. The LEDs are made of tiny nanorods arrayed in a thin film. They could enable new interactive functions and multitasking devices. The researchers report their advances in the February issue of the journal Science.

According to Moonsub Shim, Professor of materials science and engineering at the University, the new LEDs will enable displays to be much more interactive devices, rather than just displaying information as they do now. This might form the basis of several new and interesting designs for several types of electronic gadgets.

Three types of semiconductor materials make up the tiny nanorods, each of them less than 5 nanometers in diameter. The first type emits and absorbs visible light. The other two semiconductor materials control the amount of charge flowing through the first. This combination allows the LEDs to emit light, while sensing and responding to light falling on it.

By switching between the emitting and detecting modes very quickly, the nanorod LEDs can perform both functions with ease. In fact, they are so fast in switching—three times faster than the standard display rates—the display seems to be permanently on. Because the LEDs are simultaneously detecting and absorbing light as well, a display of such LEDs may be made to respond to light signals in different ways, simply by programming them suitably. For instance, a display could automatically adjust its brightness in response to ambient light conditions. Although a separate light level sensor does this for the present displays, the new display could do it by sensing the ambient light on each pixel.

According to Professor Shim, for someone sitting outside with a tablet, reading will be easier on the eye, as the tablet will adjust its brightness based on ambient light on individual pixels of the display. For instance, the part of the display under a shadow falling across it will be dimmer than the part directly illuminated by sunlight. This will help to maintain a steady contrast.

The researchers were able to program individual pixels adjust their brightness automatically in response to an approaching finger. This response, once integrated into interactive displays, could allow the display to respond to recognizing objects through non-touch gestures.

Writing or drawing with light would also be possible with such displays. This could form the basis of smart whiteboards, tablets, or other such surfaces, on which a laser stylus could write or draw. Moreover, the researchers have discovered the LEDs not only respond to light, they convert it to electricity as well.

They found the LEDs responding to light just as solar cells do. Therefore, apart from enhancing the interaction between users and displays, it is also possible to actually use the displays to harvest light, for instance, to charge the cellphone when it is simply sitting idle, collecting ambient light. That means there is no need of integrating a separate solar cell on the display.