An international research team demonstrated the possibility of tuning the color of a GaN LED by changing the time sequence at which the operation current is provided to the device.

Scientists from Lehigh University, West Chester University, Osaka University and the University of Amsterdam have collaborated to develop a new technique of color tuning for GaN LED by controlling current injection to monitor the intensity ratios of emission atomic. The research, titled “Color-Tunablility in GaN LEDs Based on Atomic Emission Manipulation under Current Injection,” was published in ACS Photonics on April 17.

(Image: West Chester University/Lehigh University )

Volkmar Dierolf, Distinguished Professor and Chair of Lehigh’s Department of Physics, who worked on the project, said, “This work could make it possible to tune between bright white and more comfortable warmer colors in commercial LEDs.”

In today’s active LED displays, different colors are produced by three to four individual LEDs that are placed close to each other and create the different fundamental colors needed to produce the full color spectrum. But with the new technique of manipulating the emission properties of an atomic-type dopant, a single GaN-based LED can achieve color-tunability.

“We demonstrate that this can be achieved by a single LED,” says Dierolf. “We show that is possible to attain red, green and blue emissions originating from just one GaN LED-structure that uses doping with a single type of rare earth ion, Europium (Eu). Using intentional co-doping and energy-transfer engineering, we show that all three primary colors can emit due to emission originating from two different excited states of the same Eu3+ ion (~620 nm and ~545nm) mixed with near band edge emission from GaN centered at ~430nm. The intensity ratios of these transitions can be controlled by choosing the current injection conditions such as injection current density and duty cycle under pulsed current injection.”

(Image: West Chester University)

Researchers further noted that the concept of the new method can also work with other LED structure and open up a new field of tunable color emission from a single dopant in semiconductors.

“It could pave the way for monolithic integration for simple color tuning of a light bulb,” adds Dierolf. “It would also be beneficial for Micro LED displays, since it allows for higher density of pixels.”

The materials used in previous research on color tunable LEDs did not allow for easy integration with current LED technology, he adds. This work is compatible with current GaN-based LEDs that are at the core of commercial solid state LED lighting.