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The 46th ROEL Lecture Session was held on Oct. 25th. Dr. Yoichi Murakami, Assistant Professor of Global Edge Institute, Tokyo Institute of Technology, was invited as a guest speaker and gave a lecture entitled "Phase-Stable Photon Upconverters based on Triplet-Triplet Annihilation of Organic Molecules".

More than 40 researchers and students attended to the lecture, and they asked many questions about the lecture in the Q&A session.

Conference room during lecture

Dr. Yoichi Murakami, Assi. Professor of Global Edge Institute, Tokyo Institute of Technology

This lecture is about organic photon upconverters that work without an external bias application and can be applicable to incoherent light such as sunlight. “Photon upconversion (UC)” is a process of converting two photons of lower energy into one photon of a higher energy. If such a technology is made possible for low intensity continuous-wave lights with meaningful efficiencies, possible range of human’s light utilizations would be significantly broadened. For example, the long-wavelength portion of solar spectrum that is currently wasted would become available for energy generation to raise the overall efficiencies of photovoltaics and artificial photosynthesis.
Whilst the UC phenomenon by triplet-triplet annihilation itself has long been known, it is only recently (since around 2006) that the efficiency exceeded 1% and then a research field is formed about this technology to pursue the application. However, since this method employs organic molecules (especially polycyclic aromatic molecules) all the meaningful reports thus far reported have employed organic solvents such as toluene and benzene. However, since such solvents possess high volatility, flammability, vapor toxicity, and incompatibility with most of polymeric materials, this point had been a major problem upon considering the application of this UC technology.
Based on the original idea and technique invented, we have developed for the first time phase-stable photon upconverters using ionic liquids, which are room-temperature molten salts that possess negligible vapor pressure and high thermal stability, and hence have solved the aforementioned problems. By this invention, non-volatile, non-flammable, long-term-stable (> 2 years), and solar-applicable photon upconverters have been realized, moving UC technology forward for application. The details will be presented in the seminar.