New glass promises improved UV blocking
By Jude Garvey
December 21, 2009
Most people are aware that ultraviolet (UV) rays can cause damage to the skin, but it can also damage the eyes. The cumulative effect of not protecting eyes from the sun can cause unpleasant problems such as cataracts, skin cancers around the eye and pterygium - an abnormal growth which starts in the corner of the eye but can grow over the cornea. Researchers from Penn State are hoping that a new recipe for making glass will further improve the protection offered by UV blocking sunglasses. The team has discovered that adding cerium oxide to phosphate glass could result in sunglasses, windows and solar cells that block UV light more effectively and have increased radiation resistance.
Traditionally, sunglasses have been made with silicate glass. In the past, cerium has been added to silicate to increase its UV absorption qualities, but silicate glass can only absorb a certain amount of cerium and begins to turn yellow when too much cerium has been added. This is not a particularly desirable effect in windows or sunglasses. However, researchers found that phosphate glass with its more flexible structure allowed more cerium to be dissolved before it began to yellow.
Jen Rygel, a researcher working on the project, together with Carlo Pantano, a professor of materials science and engineering and director of Penn State's Materials Research Institute compared and synthesized 11 glasses that had various concentrations of cerium, aluminum, phosphorus and silica. They discovered that they could create phosphate glasses that could hold 16 times more cerium oxide than silicate glasses and that the phosphate glasses maintained the ability to absorb ultraviolet light and remained colorless.
"We were able to get a lot more cerium into our phosphate glass without sacrificing the optical transmission - they both still looked clear," said Rygel.
Cerium exists in two states (cerium III and IV) in glasses. The reason phosphate glass may be capable of holding more cerium without coloring may be due to the absorption ranges of cerium (III) and cerium (IV), meaning cerium seems to absorb less blue light in phosphate glasses.
"A good example is in solar cells," said Rygel. "The wavelengths that solar cells use aren't ultraviolet, and actually ultraviolet radiation can cause damage to the electronics of a solar cell. If you add cerium to the glass you can prevent the ultraviolet from getting down to the photovoltaic cells, potentially increasing their lifetime."
The benefit of using cerium additions don’t stop at blocking ultraviolet light. It has also been shown that increasing a glass's cerium concentration can result in an increased resistance to radiation damage from gamma rays and x-rays. Rygel also discovered that cerium’s ability to block radiation was determined by the ratio of the two states of cerium in the glasses. Using x-ray photoelectron spectroscopy she discovered that all her glasses contained approximately 95 percent cerium (III).
The ability of phosphate glasses to absorb cerium promises to have commercial applications for use in sunglasses, windows, and solar cells in the future.
Via Penn State.