A New, Ecofriendly Way To Convert Blue Light to High

By Kyushu UniversityFebruary 16, 2023

UVB has many uses today but requires inefficient and toxic sources to produce. A collaborative effort involving Kyushu University and Johannes Gutenberg University Mainz developed a system where blue LED light is upconverted to UVB light. Moreover, the system uses only organic materials, opening the door for a more sustainable and eco-friendly method of generating UVB light. Credit: Kyushu University

An international team from Japan and Germany has created a system that transforms blue LED light into high-energy Ultraviolet B (UVB) light.

The new system, which does not rely on toxic and inefficient materials traditionally used for UVB production, offers a more sustainable and environmentally friendly solution for UVB applications. The findings were published in the journal Angewandte Chemie.

It is hard to avoid talk about ultraviolet light—especially during the summertime. These high-energy rays produced by the sun are outside the visible light spectrum and a well-known culprit for suntans and sunburns. UV light is subdivided into three types depending on its wavelength: A, B, and C. UVA contains the long-wave UV light that reaches the surface of Earth, whereas shorter-wave UVB and UVC are mostly absorbed by the ozone layer.

Nonetheless, scientists have found that artificially produced UVB and UVC are useful in applications such as disinfection. UVB specifically has been applied in processes including photochemical reactions, detoxification of pollutants, and wastewater treatment. It is even used in the medical field in treatments for skin disorders such as eczemaEczema, also known as atopic dermatitis, is a chronic or recurrent inflammatory skin disease. Symptoms include itchy skin; dry cracked or scaly skin, and red or brownish patches of skin." data-gt-translate-attributes="[{"attribute":"data-cmtooltip", "format":"html"}]">eczema and vitiligo.

However, generating UVB currently requires sources such as mercury lamps, which are inefficient and toxic if improperly disposed of.

One way around this is to generate UVB by ‘upconverting’ the light produced by LEDs. Upconversion is a method in which a material absorbs two photons of light of lower energy and combines their energy to emit one photonA photon is a particle of light. It is the basic unit of light and other electromagnetic radiation, and is responsible for the electromagnetic force, one of the four fundamental forces of nature. Photons have no mass, but they do have energy and momentum. They travel at the speed of light in a vacuum, and can have different wavelengths, which correspond to different colors of light. Photons can also have different energies, which correspond to different frequencies of light." data-gt-translate-attributes="[{"attribute":"data-cmtooltip", "format":"html"}]">photon of higher energy light. The method usually occurs using a series of organic materials.

Over the years, two research teams in Japan and Germany, led by Nobuhiro Yanai of Kyushu University’s Graduate School of Engineering and Christoph Kerzig of the Johannes Gutenberg University Mainz, respectively, have been working on evaluating various compounds for upconverting blue light from LEDs into UV light.

“Blue LED light’s wavelength is the closest on the visible light spectrum to UV light. We’ve had success in converting longer-wavelength blue LED light into shorter-wavelength UVA. So, our next step was to find compounds that could convert blue LED light to UVB,” explains Yanai. “With our collaborators at Mainz, we constructed candidate molecules and began screening their characteristics.”

The collaboration was a profound success, to say the least. Not only were they able to develop molecules that upconverted blue LED light into UVB, but they were also able to avoid the use of heavy metals that are traditionally used in such processes.

“Our investigations show evidence for a hitherto unreported blue-to-UVB upconversion that is also an avenue for safer and more sustainable production of UVB,” concludes Yanai. “However, this first upconversion system is liquid-based and relies on several bimolecular reactions that hamper its stability and long-term usage. Moreover, the current rate of conversion is around 1%, naturally our next goal is to increase efficiency while developing reusable materials for versatile applications.”

Reference: “Blue-to-UVB Upconversion, Solvent Sensitization and Challenging Bond Activation Enabled by a Benzene-Based Annihilator” by Till J. B. Zähringer, Julian A. Moghtader, Maria-Sophie Bertrams, Dr. Bibhisan Roy, Masanori Uji, Prof. Dr. Nobuhiro Yanai and Prof. Dr. Christoph Kerzig, 18 November 2022, Angewandte Chemie.DOI: 10.1002/anie.202215340

The study was funded by the German Research Foundation, the German Federal Environmental Foundation, and the Japan Society for the Promotion of Science.