University of California, Riverside nanotechnologists have controlled the color of very small particles of iron oxide suspended in water simply by applying an external magnetic field to the solution. The discovery has potential to greatly improve the quality and size of electronic display screens and to enable the manufacture of products such as erasable and rewritable electronic paper and ink that can change color electromagnetically.

By changing the strength of the magnetic field, the researchers were able to change the color of the iron oxide solution -- similar to adjusting the color on a TV screen. When the strength of the magnetic field is changed, it alters the arrangement of the spherical iron oxide particles in solution, modifying how light falling on the particles passes through or is deflected by the solution.

"By reflecting light, these photonic crystals show brilliant colors," said Yadong Yin, an assistant professor of chemistry who led the research. "Ours is the first report of a photonic crystal that is fully tunable in the visible range of the electromagnetic spectrum, from violet light to red light."

Photonic materials such as these could help in the fabrication of new optical microelectromechanical systems (MEMS) and reflective color display units. They also have applications in fiber optic telecommunications, sensors, and lasers.

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