Novel photochromic glass can store rewritable 3D patterns long term

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 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 1022 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.

The authors acknowledge financial support from the National Natural Science Foundation of China, Science and Technology Project of Southwest Joint Graduate School of Yunnan Province, Key Project of the National Natural Science Foundation of China-Yunnan Joint Fund, National Natural Science Foundation of High-end Foreign Experts Introduction Plan, Academician Expert Workstation of Cherkasova Tatiana in Yunnan Province, Yunnan Province Major Science and Technology Special Plan, Preparation and Property Control of Luminescent Materials and Application in Plateau Agriculture, University of Technology Sydney Chancellor's Research Fellowship Program, and the National Health and Medical Research Council.