New technique could pave the way for simple color tuning of LED bulbs

New technique could pave the way for simple color tuning of LED bulbs
Top row: A GaN:Eu LED, which can be tuned from red-yellow due to red and green light mixing from different Eu states. Middle and bottom rows: A GaN:Eu LED with additionally added Si/Mg, which adds blue emission. Each picture is under a different current injection/filtering condition. Credit: West Chester University

Volkmar Dierolf and an international team demonstrate 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.

A ―the result of an international collaboration of scientists from Lehigh University, West Chester University, Osaka University and the University of Amsterdam―could pave the way for monolithic integration for simple color tuning of a light bulb, according to Volkmar Dierolf, Distinguished Professor and Chair of Lehigh's Department of Physics, who worked on the project.

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

The team demonstrated the possibility of color tuning Gallium Nitride (GaN)-based GaN LEDs simply by changing the time sequence at which the operation current is provided to the device. Light-emitting diodes or LEDs are semiconductor devices that emit light when an electric current is passed through it. Notably, the technique is compatible with current LEDs that are at the core of commercial solid state LED lighting.

The work is described in an article published online in ACS Photonics called "Color-Tunablility in GaN LEDs Based on Atomic Emission Manipulation under Current Injection." The lead author, Brandon Mitchell, is a former graduate student in Dierolf's lab and 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 placed close to each other and create the different fundamental colors needed to produce the full color spectrum.

"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 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."

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

Mitchell pointed out that "The main idea of this work—the simultaneous active exploitation of multiple excited states of the same dopant—is not limited to the GaN:Eu system, but is more general. The presented results could open up a whole new field of tunable emission of colors from a single dopant in semiconductors, which can be reached by simple injection current tuning."

According to Dierolf, this research may benefit those who are looking for more comfortable "warmer" white light from LEDs.

"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 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.


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More information: Brandon Mitchell et al. Color-Tunablility in GaN LEDs Based on Atomic Emission Manipulation under Current Injection, ACS Photonics (2019). DOI: 10.1021/acsphotonics.8b01461
Journal information: ACS Photonics

Provided by Lehigh University
Citation: New technique could pave the way for simple color tuning of LED bulbs (2019, April 29) retrieved 23 July 2019 from https://phys.org/news/2019-04-technique-pave-simple-tuning-bulbs.html
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Apr 29, 2019
Single diode white lasers ..... yippee

Apr 29, 2019
Single diode white lasers ..... yippee

Well, stroboscope, since the implication is that the different colors are generated sequentially in pulses.

those who are looking for more comfortable "warmer" white light


The color temperature isn't the issue. You can tweak that all you want - the problem is that purely LED based lighting doesn't have a continuous spectrum. It's worse than the fluorescent tubes and generating the few primary colors by pulsing a single LED die doesn't actually solve the issue - it makes it worse.

For example, the rainbow effect created by a DLP projector is because there's a color wheel that keeps switching the primary colors at a few hundred Hertz. Anything moving under the "white" light from a DLP gets illuminated by alternate frames of red, green, blue, and appears with colored edges.

The best quality LED lights actually employ wide spectrum phosphors to fill the gaps in the spectrum. They're hybrids between LED bulbs and CFLs.

Apr 29, 2019
Here's picture of someone waving their hand in front of a DLP

https://upload.wi...fect.JPG

If your room lighting was based on rapidly switching the color of your bulbs, it would become quite psychedelic, especially if different bulbs weren't synchronized to each other. It wouldn't be instantly noticeable, but little things like colored fringes or vibration in the corner of your eye would give it away, and quite possibly the massive headaches you'd get.


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