A grad student working in a Organic LED lab in the Netherlands discovered an interesting feature in some OLEDs he was given to test:
While Dr. Hofstraat is still studying the fundamental nature of his two-tone O.L.E.D.'s, making them change color could not be easier. The color changes from red to green (or, in subsequent models, between any two primary colors) when the direction of the electrical current running through it is reversed.Red Light, Green Light: A 2-Tone L.E.D. to Simplify Screens
More from the article:
Making the O.L.E.D.'s is also simple, at least in comparison with the manufacture of silicon semiconductors. Like many organic semiconductors, the dual color Philips models are created by spraying their plastic solution out of specially designed ink jet printers.
The magic ingredient giving the Philips O.L.E.D.'s their color-switching ability is a solution of a metal known as dinuclear ruthenium. Originally, the researchers mixed it into the O.L.E.D. plastic to boost the amount of visible, rather than infrared, light that the diode creates while glowing red.
When Dr. Hofstraat studied Mr. Welter's finding, he observed that when the current headed in one direction through the diode, it excited the metal additive and created a red glow. When the direction was reversed, it was the plastic's turn to be excited by the voltage and the device glowed green. (A paper about the group's discovery appeared in the Jan. 2 issue of the journal Nature.)
By Psydeshow on January 30, 2003 at 11:28am