Ask any gem collector about Opal, and they will tell you this mineraloid material produces unique and iridescent colors that are quite attractive to the eye. What they may not know is that Opal contains a natural periodic microstructure that affects the motion of photons–in essence, a natural occurring photonic crystal. Now researchers at University of California Riverside (UCR) have demonstrated a Photonic Paper using salt water as ink to create displays that are "brilliant and free of glare in sunlight, which are superior to the characteristics of other emissive display technologies," according to a recent article by Michael Berger in Nanowerk.

Steve Sechrist
Senior Analyst and Editor

The real breakthrough in the UCR project came at several levels, first in fabricating the photonic crystals where the team moved from sedimentation or evaporation techniques that took days or even months, to an instantaneous process using an external field with magnetic particles and assembling them into periodic arrays. Assistant professor of chemistry at UCR Yadong Yin said the “periodic photonic structures can be immediately fixed in a polymer matrix. This allows for future mass production.”

Inking is achieved using a salt water solution (water-ethanol solution of inorganic hygroscopic salt) that "does not evaporate at room temperature… it keeps the polymer matrix in the swelled state so that color information stays for a long time. Erasing… is achieved by removing the salt solution using additional water," Yin said in the Nanowerk article.

Yin says that, in principle, the technique developed in his lab can potentially be used to replace conventional paper/ink systems in many areas as rewritable photonic systems have several advantages like sunlight readability, ease of large area fabrication and versatility in substrate materials (from rigid glass to flexible plastic.)

But Yin’s research goes beyond photonic paper to include Magnetochromatic Microspheres (made up of microscopic polymer beads that change color instantly). This aspect of the work is extensively covered in this month’s Mobile Display Report. Of the technology Yin said, "Our work provides a new mechanism for inducing color change in materials. Now, for the first time, stable photonic materials with tunable colors can be fabricated on a large scale. Unlike many conventional approaches, the instantaneous color change occurs with no change in the structure or intrinsic properties of the microspheres themselves. What changes instead are the magnetic fields acting externally on the orientation of these microspheres, these photonic crystals."

But the research also opens the question of a broader use of photonic band gap material as a potential replacement to semiconductors. The Nanowerk article points out photonic crystals "could play a significant role on the way to all-optical devices in communication and information technology — they form a basis material for the future realization of optical components and circuits, and maybe even complex optical circuits or optical computers." Will photons replace electrons in the future CE (err, rather CP for consumer photonic) devices and perhaps usher in the "photonic age?"