Researchers at Kyushu University in Japan have created a novel solid-state molecular material that can literally add two particles of ordinary visible light together to manufacture a single, high-energy ultraviolet (UV) photon.

Even more remarkable, it does so using nothing but ambient, unconcentrated outdoor sunlight.

This innovation achieved a 1.9 percent conversion efficiency in a solid-state system.

“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,” said Yoichi Sasaki, Associate Professor at Kyushu University’s Faculty of Engineering and the study’s corresponding author.

Race against the clock

While that number might sound modest, it is huge for material physics. Previously, pulling off this kind of quantum alchemy required blinding, high-intensity laboratory lasers. Doing it under a normal afternoon sky is a absolute game-changer.

Yet, the science is only half the story. The team had to rush their research to finish before their professor retired.

For over 14 years, Professor Emeritus Nobuo Kimizuka pursued one of the ultimate goals in molecular chemistry. He wanted to pioneer a solid-state system capable of upgrading light energy.

Liquid versions of this technology worked, but used toxic, fast-evaporating solvents. Safe solid-state alternatives existed but had issues: packing the molecules tightly together caused their energy fields to overlap and fizzle out before they could be combined.

For more than a decade, the perfect structural balance remained elusive. Then, in May 2024, a sudden spark of insight occurred in the lab.

The team engineered an organic semiconductor named dihydroindenoindenedene (DHI). Interestingly, a molecular scaffold was created by attaching tiny hydrocarbon chains to its carbon skeleton. 

It acted like microscopic spacers. The molecules were close enough to share energy, but perfectly separated so they wouldn’t neutralize each other. The system worked beautifully.

But it they had a massive problem. Professor Kimizuka was less than a year away from formal retirement. The final breakthrough had landed right at the buzzer.

What followed was a frantic scientific relay race. Working around the clock, graduate students and junior faculty condensed months of data analysis and writing into days. They finalized the manuscript and proudly handed the completed draft to Kimizuka just 11 days before his retirement.

Why a sun-powered UV upgrade matters

We usually spend our summers slathering on sunscreen to avoid harsh UV rays. So, why do scientists want to make more of it?

Industrial UV light is a foundational, invisible pillar of modern technology. It drives air purification systems. It instantly cures the resin inside high-tech 3D printers. It is the exact light energy dentists use to harden your gel fillings in seconds.

Unfortunately, usable UV light accounts for only a meager 6 percent of the natural sunlight reaching Earth.

The development turned to a phenomenon called Triplet-Triplet Annihilation (TTA) in which two excited molecules collide and pool their energy to emit a single, ultra-high-energy photon. 

First, a “donor”molecule absorbs visible light to enter a high-energy triplet state, then transfers this energy to an “acceptor” molecule. When two of these triplets collide, they annihilate each other and pool their energy to release a single UV photon. 

The team has already filed a patent for the material, noting that it features straightforward, low-cost synthesis. In the future, this sun-powered molecular film could be painted onto indoor air purifiers or used to run eco-friendly, low-intensity 3D printers using nothing but the afternoon sun.

The findings were published in the journal Nature Communications.

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