Electrochemically oxidizing and reducing an inverse polymer-gel opal causes it to swell and shrink, which alters the wavelength of the light it diffracts brightly from ultraviolet through the visible to the near infrared. Chemists Andre Arsenault, Daniel Puzzo and Geoffrey Ozin of the University of Toronto, Canada, together with Ian Manners of the University of Bristol, UK, and explain the interest in photonic crystals. These materials, made either by a chemical “bottom-up self-assembly or by a “top-down” nanofabrication approach are being envisioned as useful for a wide range of technological applications. These might include the optical transistors and waveguides of light-driven devices to new, high-efficiency and controllable light-emitting diodes (LEDs) and lasers. Read Story