Researchers at Kyushu University have developed a solid-state molecular material that converts ordinary visible sunlight into ultraviolet (UV) light. The material achieved a conversion efficiency of 1.9% under natural outdoor sunlight, as reported in Nature Communications on June 23.
The Science Behind the Breakthrough
The process used is called triplet-triplet annihilation (TTA) photo upconversion. This is a mechanism where two low-energy visible photons combine to produce one higher-energy UV photon.
The material employs an organic semiconductor, dihydroindenoindenedene (DHI). Alkyl chains are attached to sp3 carbon atoms to create controlled spacing between molecules. This structure prevents quenching of excitons while still allowing efficient energy transfer.
Performance Metrics
- Solid-state fluorescence quantum yield: Over 60%
- Photo upconversion efficiency: 1.9%
- Practical output: Approximately two UV photons are produced per hundred visible-light photons absorbed
The material is relatively simple to produce and uses inexpensive starting materials, making it a viable candidate for scalable applications.
Potential Applications
Researchers have identified several promising uses for this technology:
- Solar-driven photocatalysis
- Indoor air purification
- Low-intensity 3D printing
A patent application has been filed to protect the invention.
Research Background
This project builds on over 14 years of research at Kyushu University, initiated by Professor Emeritus Nobuo Kimizuka.
The work was completed by graduate students Naoyuki Harada, Hayato Shoyama, and Nutnicha Boonmong, along with Assistant Professor Kiichi Mizukami and Associate Professor Yoichi Sasaki.