What is remarkable about the nanoparticles is that they are similar to the gold compounds used in medieval times to create stained glass, as used for the windows of churches and cathedrals. The light-scattering properties of the gold particles produced glass with rich red tones.
A research group has found a way to trigger nanoparticles to scatter bright light in various colors. The key to achieving this is by using metal nanoparticles capable of absorbing light energy and converting it into plasmons. Plasmons are waves of electrons that flow like a fluid across a particle’s surface. Each plasmon scatters and absorbs a characteristic frequency of light; by varying the plasmonic frequency different colors can be created.
Plasmonics refers to the study of the interaction between an electromagnetic field and free electrons in a metal. Certain metals, like copper and gold, have specific electronic inter-band transitions; here specific light energies (colors) are absorbed and distinct colors produced.
To create a working model, researchers connected pairs of gold nanoparticles onto a glass surface. The surface was coated with indium tin oxide (ITO). ITO is used as a conductor on the display screens of most smartphones. The particles are sealed in a chamber filled with a saltwater electrolyte and a silver electrode to create a circuit and electrochemical bridging. By changing the current, different colors are formed. The change of color is reversible.
If the technology can be produced commercially, this would allow users to deploy standard electrical switching techniques to create color displays from pairs of nanoparticles that scatter different colors of light. Such technology would enable tiny, fast, and efficient components to be created for displays.
The research was conducted by Christy Landes, associate professor of chemistry at Rice University and the findings are published in the journal Science Advances. The research paper is titled “From tunable core-shell nanoparticles to plasmonic drawbridges: Active control of nanoparticle optical properties.”
