Sunlight just got an upgrade: Scientists have developed a material that converts ordinary sunshine into UV light, opening new possibilities for solar-powered technologies.
Imagine pouring two cups of warm water together and expecting to get one cup of boiling water. That is impossible in everyday life, but something similar can happen in the quantum world. There, two low-energy particles of light, known as photons, can combine their energy to create a single photon with much higher energy.
Researchers at Kyushu University have now developed a solid-state molecular material that can convert ordinary visible sunlight into ultraviolet (UV) light. The material achieved a conversion efficiency of 1.9% under natural outdoor sunlight. Their findings were published in Nature Communications on June 23.
Converting Visible Sunlight Into UV Light
Although most people try to avoid UV exposure during the summer, ultraviolet light plays an essential role in many technologies. It is used for air purification, curing resins in 3D printing, and hardening gels in dental fillings and nail products. Even so, UV light makes up only about 6% of the sunlight that reaches Earth’s surface, and only part of that small amount is useful for practical applications.
“What we do here is ‘add together’ the energy from two visible light photons to make one ultraviolet photon. It’s a fascinating process called photo upconversion,” explains Yoichi Sasaki, Associate Professor at Kyushu University’s Faculty of Engineering and the study’s corresponding author.
One way to achieve photo upconversion is through a process called triplet-triplet annihilation (TTA). In this process, a “donor” molecule absorbs visible light and moves its electrons into a high-energy triplet state. That energy is then transferred to a nearby “acceptor” molecule. When two triplet states come together, they combine their energy and release it as a single UV photon.
This approach works well in liquids because molecules can move freely, allowing the triplet states to meet more easily. However, liquid systems often require toxic solvents and can evaporate, making them less practical for real-world applications. For years, researchers have searched for an effective solid-state alternative.
Designing a Better Solid State Material
“In solids, molecules are packed tightly, and the π electron clouds—regions of high electron density hovering above and below each molecular plane—can overlap,” says Sasaki. “When that happens, triplets easily fizzle out before they ever meet. Molecules must be close enough for energy to transfer but separated enough to prevent quenching of excitons.”
To overcome this problem, the researchers turned to an organic semiconductor called dihydroindenoindenedene (DHI). They attached alkyl chains to DHI’s sp3 carbon atoms, which have four bonds pointing in fixed 3D directions. This design created carefully controlled spacing between neighboring molecules, keeping them close enough to transfer energy while preventing the strong electronic interactions that reduce efficiency.
The resulting material produced bright light emission, maintained long-lived excited states, and transferred energy efficiently. It also achieved a solid-state fluorescence quantum yield of more than 60%. When paired with a donor molecule, it reached a photo upconversion efficiency of 1.9%.
“This means roughly two UV photons are produced for every hundred visible-light photons absorbed,” Sasaki adds. “It may sound low, but it runs on natural sunlight alone. Most solid-state materials cannot realize this even at much higher light intensity.”
Potential Uses for Sunlight-Powered UV Light
The team has filed a patent application for the new material. In addition to its performance, the material is relatively simple to produce and relies on inexpensive starting materials. The researchers believe it could eventually be used for solar-driven photocatalysis, indoor air purification, and low-intensity 3D printing.
A Breakthrough More Than a Decade in the Making
For the researchers, the project represents more than a scientific achievement.
In 2012, Nobuo Kimizuka, now Professor Emeritus at Kyushu University’s Research Center for Negative Emissions Technologies, began pioneering work on photon upconversion through triplet energy migration in self-assemblies. His goal was to develop molecular systems in which self-assembly performs useful functions. Over the years, his team made significant progress using solutions and gels, but creating an efficient solid-state system remained an unsolved challenge.
That changed in May 2024, less than a year before Kimizuka retired.
Graduate students Naoyuki Harada, Hayato Shoyama, and Nutnicha Boonmong, together with then Assistant Professor Kiichi Mizukami of Kyushu University’s Faculty of Engineering, joined Sasaki in an intensive effort to bring years of research together.
“We handed the draft to Professor Kimizuka just 11 days before he left the lab, which for us felt like a heartfelt retirement gift,” Sasaki notes.
“This discovery is the culmination of over 14 years of our research and marks a major milestone in photon-upconversion and molecular self-assembly research,” concludes Kimizuka.
Reference: “Sterically protected π-electron systems for efficient solid-state photon upconversion” by Naoyuki Harada, Hayato Shoyama, Nutnicha Boonmong, Kiichi Mizukami, Yuya Watanabe, Pei Zhao, Masahiro Ehara, Yoichi Sasaki and Nobuo Kimizuka, 23 June 2026, Nature Communications.
DOI: 10.1038/s41467-026-73898-0
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