Penn State discovers new type of optical glass

09 Apr 2019

Novel germanosilicate glass range made by adding zinc oxide exhibits good lens properties.

A new composition of germanosilicate glass created by adding zinc oxide has properties good for lens applications, according to researchers at Penn State University, Pa, U.S., who say this achievement "marks the discovery of a novel glass family."

The researchers invented a new family of zinc germanosilicate glasses that have a high refractive index comparable to that of pure germania glass. The samples also exhibit high transparency, good ultra-violet-shielding properties, and good glass forming ability, making them suitable for lens applications. They published their results in the Journal of Non-Crystalline Solids.

Germanosilicate glass is essential in the manufacture of optical amplifiers, waveguides, and solid-state lasers.

"The motivation for the study was the need for new glass compositions that have a high refractive index while still being processable at an industrial scale," commented John Mauro, professor of materials science and engineering at Penn State.

A glass's refractive index determines its potential use in optical applications. "The benefit of a high refractive index is its capacity for designing low-thickness lenses," said Ye Luo, doctoral student in materials science and engineering.

In glass synthesis, however, there are certain barriers to achieving a high refractive index. Lead oxide can accomplish this, but it requires the use of toxic raw materials. Non-lead constituents that encourage a high refractive index can make the glass much more difficult to form, or prone to crystallization and therefore more opaque. By finding the optimum balance of zinc oxide with the other components of the glass composition, the researchers were able to avoid these issues.

UV shielding

Zinc oxide demonstrated useful UV shielding properties in the study samples. This should not be surprising, Mauro said, given that inorganic sunscreen is based on zinc oxide. With UV shielding, a zinc-oxide-containing glass could be used for everyday applications such as car windows or eyeglasses.

The glass samples also showed favorable forming properties. As a "long glass," the new compositions can be formed over a broader temperature range, making them much simpler to manipulate during formation. This property, the resistance to crystallization, and the lower cost of zinc oxide compared to germania all make this new glass composition a practical choice for manufacturing on a mass scale, the researchers said.

The researchers have now filed a patent for the zinc oxide-containing germanosilicate glass.

Pouring the glass

The following Penn State video shows Ye Luo, PSU doctoral student, pouring the new composition of germanosilicate glass into an optical component mold: