Artificial photosynthesis
How human use sunlight may alter if there is a solid substance that ‘upconverts’ visible light photons to UV light photons.
The importance of solar power as a renewable energy resource is increasing. Sunlight contains high-energy UV light with a wavelength shorter than 400 nm, which can be broadly used.
For example, for photoploymerisation to form a resin and activation of photocatalysts to drive reactions that generate green hydrogen or useful hydrocarbons as such fuels, sugars, olefins, etc.
The latter of these is often called artificial photosynthesis. Photocatalytic reaction by UV light to efficiently kill viruses and bacteria is another important application.
Unfortunately, only about 4% of terrestrial sunlight falls within the UV range in the electromagnetic spectrum. This leaves a large portion of sunlight spectrum unexploited for these purposes. Photon upconversion(UC) could be the key to solving this problem
Photon upconversion as triplet-triplet annihilation
Photon upconversion is the process of converting long-wavelength, low-energy photons such as those present in visible light to short-wavelength, hIgh-energy photons such as those present in UV light via a process called triplet-triplet annihilation(TTA).
Previous work in this field has reported visible to UV UC using organic solvent solutions that required the solution to be deoxygenated first and then sealed in an airtight container to prevent exposure to oxygen that deactivated and degraded TTA-based photon UC samples.
https://www.eurekalert.org/news-releases/978123
These materials not only lacked photostability in the presence of oxygen, but also failed to perform effectively with sunlight-intensity incident light. These issues present roadblocks in the practical application of photon UC.
Now two scientists at Tokyo Tech, Prof. Yoich Murakami and his graduate student Riku Enomoto have come up with a resolution to these problems. A revolutionary solid film that can perform visible-to UV photon UC for weak incident light while remaining photostable for an unprecedented amount of time in air.
They describe this breakthrough invention in their paper published in the Journal of Materials Chemistry C, they detail their ground-breaking idea. In the originality of their study, their creation will make it possible to use low-intensity visible light, such that from the sun and LED room lightening, for tasks that can only be done successfully with UV light.
Additionally, its photostability which has been shown to be at least over 100 hours even in the presence of air is the greatest ever recorded in any TTA-based photon UC material, whatever of the material form, for as long as we could search.
TTA-based photon UC film
These film also had an extremely low excitation threshold only 0.3 x the sun’s intensity and a high UC quantum yield of 8.6%, both in the presence of air. This made these film unique because most materials in this class lose their photon UC ability when exposed to air.
In order to create this material, the researchers combined a sensitizer, a molecular chromophore that can absorb longer-wavelength photons with a significantly larger amount of an annihilator, an organic molecule that received the triplet-excited energy from the sensitizer and then caused the TTA process.
A solid-state visible-to UV photon UC thin film was created from this bi-component melt by cooling it over a surface with controlled temperature gradient.
Temperature gradient solidification is an unique method that is extremely repeatable and controlled, making it appropriate for use with actual industrial processes.
This work shows for the first time that the temperature-controlled solidification may offer a solid foundation for building improved photon UC films, that too on a strong substrate without employing organic solvents.
Finally, the researchers employed a 1-sun-intensity simulated sunshine made up of visible light to effectively cure and harden a resin that would normally require UV light for the same procedure to show the thin film’s visible-to-UV phOton UC.
Source: Eureckalert
