Researchers at the University of Osaka and Ritsumeikan University coaxed blue, green, yellow and red light from a single terbium-doped nitride layer, with no measurable color drift as the current changed.

Look closely at almost any color screen and you will find the same basic trick. Each pixel is built from separate red, green and blue light sources, and the display mixes them in different proportions to produce every other hue. That arrangement works well for phones and televisions, but it becomes a serious engineering headache as pixels shrink toward the scale needed for smart glasses and other near-eye displays.

A team from the University of Osaka and Ritsumeikan University in Japan now reports a different approach. In a study published in Applied Physics Letters, the researchers describe light-emitting diodes in which a single light-emitting layer produces blue, green, yellow and red light at room temperature, and in which those colors do not drift as the driving current changes.

“We demonstrated multiple colors from one light-emitting layer, together with exceptional stability as the current changed,” said senior author Shuhei Ichikawa.

The trouble with tiny pixels

The work is aimed at micro-LED displays, an emerging technology in which each pixel is made of microscopic inorganic LEDs. Micro-LEDs promise high brightness, efficiency and resolution, which is why they are widely seen as a candidate for augmented-reality glasses and other compact screens that must remain visible in daylight.

Many premium phones and televisions today use OLED screens, in which each pixel is made of organic light-emitting materials. Micro-LEDs use inorganic semiconductor crystals instead, which tend to be brighter and longer-lasting. Their main obstacle has been manufacturing, because each display requires enormous numbers of microscopic chips that must all work and be placed precisely.

Most blue and green LEDs today are made from nitride semiconductors, the family of materials behind the blue LED whose invention earned Isamu Akasaki, Hiroshi Amano and Shuji Nakamura the 2014 Nobel Prize in Physics. Producing longer wavelengths from these materials usually means adding more indium to the light-emitting layer, and that brings problems. According to the release, conventional green and red nitride LEDs shift color as the current increases, which complicates precise color control.

Building a full-color micro-LED display also typically requires separate light-emitting layers or separately fabricated red, green and blue chips. At larger scales, manufacturers can make the three types separately and place them side by side. But as each pixel shrinks, picking, aligning and bonding millions of tiny chips becomes increasingly difficult, and packing many pixels into a small area gets harder.

Borrowing light from a rare earth

Instead of tuning the semiconductor itself, the Osaka team let a rare-earth element do the work. The researchers built aluminum gallium nitride (AlGaN) LEDs doped with terbium ions, using a nitride fabrication method that is already widely used. When driven electrically, the terbium ions emitted blue, green, yellow and red light from the same area of the device.

Terbium is no stranger to lighting. Its ions are prized for their bright green glow and have long been used in phosphors, including those in fluorescent lamps. Rare-earth ions emit light through transitions of electrons in an inner shell that is partly shielded from its surroundings, so the wavelengths they produce are sharp and largely fixed by the ion rather than by the host material. The University of Osaka has a long record of research on rare-earth-doped nitride LEDs, including europium-doped gallium nitride for red emission.

That shielding helps explain the key result. When the researchers changed the current, they found no detectable shift in the emission peaks within the measuring instrument’s 0.6-nanometer resolution.

In a conventional nitride LED, by contrast, the color is set by the energy gap of the semiconductor’s light-emitting layers, and that gap is sensitive to operating conditions. As the current rises, internal electric fields are partly screened and electronic states fill up, nudging the emitted wavelength. In green LEDs, the result is a noticeable shift toward bluer light at higher currents.

Tuning the host

The team also found that the composition of the host semiconductor mattered. Increasing the aluminum content improved the transfer of energy from the semiconductor to the terbium ions. The best device reached an external quantum efficiency up to 10.3 times higher than that of the lowest-aluminum device the researchers tested.

External quantum efficiency is the share of electrons passing through an LED that end up as photons leaving the device, so improving it is central to making a practical display.

Aluminum gallium nitride is itself a familiar material. With enough aluminum, it emits deep ultraviolet light, and it is the basis of the ultraviolet LEDs now used in some water and surface disinfection systems. In the Osaka devices, however, the semiconductor acts mainly as a host that passes energy to the terbium ions.

The foundation also proved important. Growing the LEDs on an aluminum nitride base layer improved crystal quality and device performance, by better matching the light-emitting material to the layer beneath it and reducing defects. Because all of the colors come from the same area, the researchers used color filters to separate the red, green and blue components of the output.

Simpler pixels, eventually

According to the release, the single-layer approach could simplify the integration of several colors into one micro-LED and reduce the need to assemble separate red, green and blue chips. That could matter most where pixels are smallest and alignment tolerances tightest.

The authors are clear that the technology is at an early stage. In its current form, the device emits all four colors at once, and the release notes that efficiency and control over the brightness of each color both need improvement before it could be used in a display.

“Our next goal is to improve the efficiency and control the intensity of each color,” Ichikawa said.

If those hurdles can be cleared, the researchers see potential applications in smart glasses, wearable devices, compact high-resolution displays and white-light sources. For now, the study offers a proof of principle that a single, conventionally manufactured nitride layer can serve as a stable source of several colors at once.

The research was supported by the Japan Society for the Promotion of Science and the Japan Science and Technology Agency.

---

Notes

1. “Ultra-stable multiple emission wavelengths produced by Tb-doped AlxGa1-xN-based light-emitting diodes.” Applied Physics Letters, 1 July 2026. DOI: 10.1063/5.0331734.
2. The University of Osaka. “One LED, four stable colors.” EurekAlert!, 27 July 2026. https://www.eurekalert.org/news-releases/1138155.