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.