Scientists have known for years that ultraviolet light can kill many viruses and bacteria. Researchers at the UC Santa Barbara Solid State Lighting and Energy Electronics Center report they are taking that knowledge and using it to create light emitting diodes in the UV spectrum that could sanitize surfaces that may have been contaminated with the COVID-19 virus.
First, a primer. Electromagnetic radiation is composed of many wavelengths. Some are used for radio communications, either AM or FM, others are used to cook food in a microwave oven. The human eye reacts to some electromagnetic wavelengths, which allows us to see the world around us. The visible spectrum ranges from red to violet. Any wavelengths longer than red are called infrared — below red. Any wavelengths shorter than violet are called ultraviolet — above violet. None of this has anything to do with the bands Deep Purple or Purple Haze. Got that? Let’s move on.
Killing Virus With Light
While some scientists rush to discover a vaccine that is effective against the COVID-19 virus, others are working to discover new ways to sanitize areas that may have the virus on their surfaces. Wiping door handles and light switches with disinfectant is all very good, but how do you reach deep into ventilating systems where the virus could be hiding?
Ultraviolet LEDs could be one solution. Christian Zollner, a doctoral candidate at UC Santa Barbara says, “One major application is in medical situations — the disinfection of personal protective equipment, surfaces, floors, within the HVAC systems, et cetera.”
The work at UC-SB is supported by many corporate partners. One of them is Seoul Semiconductor, which reported last week a “99.9% sterilization of coronavirus (COVID-19) in 30 seconds” with its UV LED products. The technology currently is used to make UV LED lamps that sterilize the interior of unoccupied vehicles.
What we call ultraviolet is actually three different segments of the EM spectrum. UV-A and UV-B are the ones commonly supplied to the Earth by the sun. UV-C is the most effective as a disinfectant but does not occur in nature. It has to be created by humans.
“UV-C light in the 260 – 285 nm range most relevant for current disinfection technologies is also harmful to human skin, so for now it is mostly used in applications where no one is present at the time of disinfection,” Zollner said. In fact, the World Health Organization warns against using ultraviolet disinfection lamps to sanitize hands or other areas of the skin — even brief exposure to UV-C light can cause burns and eye damage.
At the present time, most UV-C comes from mercury vapor lamps and research into creating it with LEDs is must getting started. “Many technological advances are needed for the UV LED to reach its potential in terms of efficiency, cost, reliability and lifetime,” Zollner says.
A Research Breakthrough
In a research note published by the journal ACS Photonics in January, the researchers reported a more elegant method for fabricating high quality UV-C LEDs. It involves depositing a film of aluminum gallium nitride on a substrate of silicon carbide instead of the more widely used sapphire substrate.
According to Zollner, using silicon carbide allows for more efficient and cost effective growth of high quality UV-C semiconductor material than does sapphire. “As a general rule of thumb, the more structurally similar (in terms of atomic crystal structure) the substrate and the film are to each other, the easier it is to achieve high material quality,” he says. It is also much less expensive.
Portable, fast-acting water disinfection was one of the primary applications the researchers had in mind when developing their UV-C LED technology. The diodes’ durability, reliability, and small size make it ideal for areas of the world where clean water is unavailable. But disinfecting areas that may be contaminated by the coronavirus is opening a new window of opportunity for the technology. “This would provide a low cost, chemical free, and convenient way to sanitize public, retail, personal, and medical spaces,” Zollner says.
There’s Only One Problem
Perfecting the process will require extensive time in the lab and right now, in a delicious bit of irony, the labs at UC-SB (and everywhere else) are shut down because of the very virus the technology could be effective against. “Our next steps, once research activities resume at UC-SB, is to continue our work on improving our AlGaN/SiC platform to hopefully produce the world’s most efficient UV-C light emitters,” Zollner says. Let’s hope that resumption comes soon.
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