A Bright Idea

Sarah Fobes ’12 and Zane Glauber ’12
Sarah Fobes ’12 and Zane Glauber ’12
Standing in the dark lab, Sarah Fobes ’12 and Zane Glauber ’12 flip the switch to turn on their laser. In the blink of an eye, the tiny glass sample that they had labored over glows a radioactive green—with any luck, a brighter green than the last one they illuminated. Working with Professor of Physics Ann Silversmith, Fobes and Glauber are spending the summer experimenting with different aspects of glass formation to make it fluoresce (or glow) more brightly, with the indirect consequence of being able to make a better laser.

When illuminated, the glasses look like Hollywood’s interpretation of a radioactive substance, although they are not at all radioactive. Because they enrich the glass with different elements, each wavelength (and resulting color) fluoresces differently; terbium, for instance, glows bright green (other elements that they use include praseodymium, erbium, thulium, and holmium). Glauber and Fobes also experiment with various chemical additives that change their samples’ interactions with light.

The team is infusing the glass with different concentrations of rare earth elements. Rare earth elements are usually silver in color and have a high luster, but their most important quality as far as the team is concerned is their unique energy level configuration such that all of these rare earth metals are more or less indifferent to their surroundings. “This is useful because then they behave the same even if we vary the glass we put them in,” Fobes says. But the process of making these glasses has many factors besides the variable components.

To form regular glass, sand is melted and then crystallizes as it cools. Instead of using sand, which is made mostly of silica (often in the form of quartz), the team is using a method of glass preparation called “solution-gelation”, or simply “sol-gel”. A synthetic material called tetramethyl orthosilicate (or TMOS) forms the basis for the initial solution, which is then dried to become a gel. TMOS is toxic, potent and reacts very quickly with water, but it shares the same silica framework as melted sand. By using TMOS, the researchers can make glass more easily and efficiently and can also ensure the specific components and concentrations of the other substances they add.

There are a few challenges with preparing glass using this method. The first is that the gels must be heated to high temperatures to become glass, and often the high temperatures cause the gels to crack. Also, because sol-gel glasses are porous, water from the air is able to diffuse back into the sample, a process called “quenching.” Both of these result in reduced fluorescence. The team is doing dozens of trials this summer in the hope of making a denser—and, thus, less porous— glass that also doesn’t crack when it is heated.

So far, the team has discovered that the sample infused with terbium reliably emits light at a wavelength of 542 nanometers—bright green light to the human eye. The exceptional reliability of the wavelength of the emitted light is useful for the development of lasers; lasers are concentrated emission of light with a specific frequency. The more reliably the source can emit that frequency, the better—and more dependable—the laser. Lasers have many different uses, ranging from military technology to dermatology and ophthalmology; lasers that emit light at a wavelength of 542 nanometers (like the glass in Fobes’ and Glauber’s project) are used for healing vascular skin lesions, which can be serious if left untreated.

Sarah Fobes has a double major in mathematics and physics. Outside the lab, she spends much of her free time dancing; she runs the Latin dance club Tropical Sol as well as the Ballroom Dancing Club.

Zane Glauber, also a math-physics double major, is a member of the Champion club ice hockey team on campus and also enjoys playing the drums in his spare time. He will be spending the fall semester at the University of Sussex in Brighton, England.

Sarah Fobes '12 is a graduate of Hopkins High School (Minn.) and Zane Glauber '12 graduated from The Fox Lane High School (Bedford, N.Y.).
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