A new technique could pave the way for a simple color adjustment of LED bulbs

Volkmar Dierolf and an international team demonstrate the ability to adjust the color of a GaN LED by changing the time sequence at which the operating current is supplied to the device.

A new technique, an outcome of an international collaboration between scientists from Lehigh University, West Chester University, Osaka University and the University of Ottawa. University of Amsterdam, could pave the way for a monolithic integration for the simple tuning of the colors of a light bulb, according to Volkmar Dierolf, distinguished Professor and Director of the Lehigh Physics Department, who worked on the project .

"This work could help to make bright white and warmer colors more comfortable in commercial LEDs," says Dierolf.

The team has demonstrated the ability to tune Gallium Nitride (GaN) GaN GaN colors by simply changing the time sequence at which the operating current is supplied to the device. Light emitting diodes (LEDs) are semiconductor devices that emit light when an electric current passes through them. This technique is particularly compatible with the current LEDs which are at the heart of LED commercial solid-state lighting.

The work is described in an article published online in Photonics ACS called "Color-Tunablility in GaN LEDs based on the manipulation of atomic emission under current injection." The lead author, Brandon Mitchell, is a former graduate student of Dierolf Lab and is now an assistant professor in the Department of Physics and Engineering at West Chester University in Pennsylvania.

In today's active LED displays, different colors are produced by three to four individual LEDs that are close to each other and create the different fundamental colors needed to produce the full color spectrum.

"We demonstrate that this can be achieved with a single LED," says Dierolf. "We show that it is possible to obtain red, green and blue emissions from a single GaN LED structure using doping with a single type of rare earth ion," he says. 39, Europium (Eu) Using the intentional engineering of co-doping and energy transfer, we show that the three primary colors can emit due to emission from two excited states different from the same Eu₃⁺ ion (~ 620 nm and ~ 545nm) mixed with near-GaN band edge emission centered at ~ 430nm. The intensity ratios of these transitions can be controlled by choosing the current injection conditions, such as the injection current density and the duty cycle under pulsed current injection. "

In other words, the team achieved color tunability in a single GaN-based LED by manipulating the emission properties of an atomic type dopant.

Mitchell pointed out that "the main idea of ​​this work – the simultaneous active exploitation of several excited states of the same dopant – is not limited to the GaN: Eu system, but is more general.The results presented could open a whole new field tunable color emissions of a single dopant in semiconductors, which can be achieved by a simple adjustment of the injection current. "

According to Dierolf, this research could benefit those looking for a warmer "warmer" white light from LEDs.

"This could pave the way for monolithic integration for simple color adjustment of a light bulb," adds Dierolf. "This would also be beneficial for micro-LED displays because it allows a higher density of pixels."

The materials used in previous research on adjustable color 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 heart of commercially available semiconductor LED lighting.