In the quest for more efficient PV cells, OLED displays, and anti-cancer therapies, researchers worldwide have been focusing on the up-conversion of two low-energy photons into a single high-energy photon. This process involves the absorption of light by a material, where the energy is passed among the molecules as triplet excitons. However, the challenge has been in understanding how two triplet excitons can effectively combine their energies to emit a high-energy photon from a single molecule.

Kobe University photoscientist Kobori Yasuhiro and his research group have made significant progress in this area by studying the electron spin states of moving and interacting excited states. Their research has shown that the alignment of electron spin states of two triplet excitons is crucial for the transfer of energies to a light-emitting molecule. This alignment is dependent on the relative orientation of the molecules involved in the process.

By utilizing a thin-film solid-state material that allows for the observation of magnetic properties of electron spins and generates sufficient triplet exciton concentrations, Yasuhiro and his team were able to directly observe the time evolution of the electron spin state inside up-conversion materials. This observation led to the development of a new theoretical model that explains how the electron spin state is related to the up-conversion process.

The results of their study, published in The Journal of Physical Chemistry Letters, provide a guideline for designing highly efficient photon up-conversion materials based on the microscopic mechanism of the process. It was discovered that for the efficient transfer of energies to a light-emitting molecule, the electron spin states of two triplet excitons must be aligned. This alignment is facilitated by the ability of the triplet excitons to move around between molecules of various orientations.

The newfound knowledge of the up-conversion process’s microscopic mechanism is expected to have far-reaching implications beyond the development of high-efficiency solar cells. Yasuhiro believes that this understanding can be applied to photodynamic cancer therapy and diagnostics that utilize near-infrared light for optical up-conversion without causing harm to the human body. The potential applications of this research extend into a wide range of fields, promising advancements in energy solutions and healthcare technologies.

Physics

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