UCSB researchers work to improve disinfection with LEDs
While medical experts around the world search for a vaccine, researchers at UCSB are examining the potential role ultraviolet light plays in disinfecting various materials from the ruthless coronavirus.
According to a UCSB news release, “The COVID-19 outbreak brought with it an almost immediate and unprecedented national shortage of personal protective gear needed by health-care workers and others seeking to prevent the spread of the virus. N95 masks intended for single use by frontline health workers were being cleaned and reused. Questions arose: Were they clean? Were they safe? Were they still effective?”
To answer those questions, as well as to decontaminate shared surfaces and spaces and neutralize the virus in recirculated air, researchers at the Solid State Lighting and Energy Electronics Center (SSLEEC) in UCSB’s College of Engineering are using their expertise to develop Light Emitting Diode (LED) lights that emit ultraviolet wavelengths of 200-280 nanometers (UVC).
This special UVC light is important to fighting COVID-19 because according to UCSB, “While we receive ultraviolet light in the form of UVA and UVB from the sun, UVC, the ultraviolet light of choice for purifying air and water and for inactivating microbes, can be generated here only via man-made processes.”
Although UVC light has been used for more than 40 years to disinfect drinking water, it must be used properly for it to be safe for human eyes and skin.
According to the International Ultraviolet Association, “This UVC light is much ‘stronger’ than normal sunlight, and can cause a severe sunburn-like reaction to your skin. The target tissue in the eye would be the cornea (rather than the retina). It’s unlikely that any of the UVC light would penetrate through the cornea and then lens to reach the retina because of the short wavelength (i.e. high frequency).”
Steve Denbaars, UCSB Materials Science professor and SSLEEC co-director, is one of three UCSB researchers leading the project. The others are UCSB materials professors James Speck and Shuji Nakamura, a Nobel Laureate.
Mr. Denbaars said in the news release that with powerful and efficient UVC LEDs,“you could pass air through a light tunnel to decontaminate it; you just need enough photons to hit enough of the air. It used to be that people thought it would be nice to have contamination devices on subways and ships and other enclosed spaces where people gather in large numbers. The coronavirus has made it a priority.”
Due to the nature of their work, when campus labs were ordered to temporarily close in response to COVID, SSLEEC’s UV projects were among those selected as “essential research.”
“You have a tipping-point application, because you can’t decontaminate an entire room by spraying, and you can’t decontaminate your food by spraying it with Clorox. You can’t even decontaminate your mask with Clorox, or with alcohol,” Mr. Denbaars said in a statement. “But you can decontaminate it with UV light. The other way to decontaminate masks is to use vapor hydrogen peroxide, but to do that you have to buy a special reactor made for hydrogen peroxide, which is expensive, and that process allows you to use the mask only about three times.”
While he finishes up his doctorate in materials science at UCSB, Chris Zollner has been working on the UV project for more than three and a half years.
As one of the original students working on the project preCOVID-19, Mr. Zollner said once they were presumed as “essential research” he was joined by other doctorate students at UCSB to help work on the project.
“We definitely had a sense right at the beginning that this was going to be big,” Mr. Zollner said.
Mr. Zollner told the News-Press about the effectiveness of using LED lights to generate UVC, compared to older, traditional lights.
He said just like with household lights, LED lights outperform regular light bulbs in almost every single case. According to Mr. Zollner, UVC decontamination lights have normally been generated using mercury-vapor lamps, which require a lot of voltage to run and carry the risk of breaking and releasing mercury.
UVC LED lights, on the other hand, solve the problems associated with mercury-vapor lamps because they require little power to run, are small, hard to break and nontoxic.
However, according to UCSB’s press release, “Currently, LEDs emitting UVC light are only about 3% efficient, making them most effective for low-power portable applications, as seen in some UV LED-equipped water bottles, while the LED light bulb you buy at the store is about 60% efficient.”
To improve the efficiency of UVC LED lights, UCSB researchers are using metal organic chemical vapor deposition (MOCVD) to grow semiconductor materials that will allow them to adjust the amount of UVC light emission.
According to the press release, “Together they have developed a new material, made by depositing a thin film of the semiconductor alloy aluminum gallium nitride (AlGaN) on a silicon substrate.”
Mr. Zollner explained to the News-Press that other UVC LEDs use sapphire while their new method works by replacing sapphire with silicon carbide.
“Current UVC disinfection lamps, such as mercury vapor lamps, have fixed light emission of 254 nanometers,” Mr. Denbaars said in a statement. “However, many bacteria, fungi and viruses are killed more efficiently at different wavelengths. The AlGaN material system being developed at UCSB allows for greater flexibility in fine-tuning UVC light emission from an LED, which would make targeting specific microorganisms a real possibility. Aluminum gallium nitride is the only semiconductor that provides light of the correct wavelength, and UCSB is a world leader in developing it.”
As they work to find a way to make UV LED lights more efficient, going forward, Mr. Zollner said he believes the current circumstances will lead to more research being done surrounding UV LED technology.
He said the goal is to produce and use shorter wavelengths that are safe for people.
“The goal is to shift to certain shorter wavelengths of UV that are safe for skin and eyes, so you could have safe decontamination even in the presence of people,” Mr. Denbaars said in a statement. “You could leave the lights on all the time for applications like hospital operating tables, Navy ships and submarines, airplanes, prisons and so on. I think we’re years, not decades, away from that.”