Novel photochromic glass can store rewritable 3D patterns

For decades, researchers have been exploring how to store data in glass because of its potential to hold information for a long time—eons—without applying power. A special type of glass that changes color in different wavelengths of light, called photochromic glass, holds promise for stable, reusable data storage.

Now, researchers have developed a doped photochromic glass that has the potential to store rewritable data indefinitely, according to research published in ACS Energy Letters.

Certain types of eyeglasses get darker when exposed to wavelengths of light emitted by the sun and then shift back to a colorless lens indoors when no longer exposed to those light waves through a process called reversible photochromism.

Likewise, other types of photochromic glass can switch color in response to different wavelengths of light, making this material attractive as an inexpensive and stable platform for storing vast amounts of information in a small space. But the challenge in using photochromic glass for data storage involves not only writing information into the glass but also erasing and rewriting it ad infinitum.

Now, Jiayan Liao, Ji Zhou, Zhengwen Yang and a multidisciplinary team have made progress toward this goal by creating reversible, tunable patterns on photochromic gallium silicate glass.

The team first designed gallium silicate glass modified with magnesium and terbium ions by using a process called doped direct 3D lithography. Liao and the team used a green 532-nanometer (nm)-wavelength laser to inscribe 3D patterns into tiny slabs of the doped glass.

The intricate patterns, randomly chosen dots, symbols, QR codes, geometric prisms, and even a bird, appear purple in the transparent glass, which turns into other colors when excited at precise wavelengths. Terbium luminesces green when excited by a deep violet 376-nm laser, and magnesium luminesces red in the presence of violet light at 417 nm.

Then, to fully erase the patterns without changing the structure of the glass, the team applied heat at 1,022 degrees Fahrenheit (550 degrees Celsius) for 25 minutes.

Furthermore, the researchers consider the use of magnesium and terbium groundbreaking for their abilities to luminesce at distinctly different wavelengths, which makes it possible to get a tunable, multicolor readout of 3D patterns from a single material. The new approach could be used for high-capacity, stable 3D optical memory storage and encryption in industrial, academic and military applications.