Phosphorescence boosts solid-state lighting
R Colin Johnson
2/14/2011 4:08 PM EST
PORTLAND, Ore.— Switching to purely organic phosphorescent emitters could drastically cut the cost of solid-state lighting panels, according to a team of researchers at the University of Michigan. The team claims to have found the first example of a purely organic—and thus ultra-cheap—compound that can compete with an metal-doped emitters in terms of brightness and color tuning capability.
Unlike fluorescence, a phosphorescent material does not immediately re-emit the radiation it absorbs, but rather continues to glow for up to several hours after the original excitation—a property that has previously been seen only in compounds doped with metals, called organometallics. However, these new metal-free organic compounds developed at the University of Michigan, which appear white in visible light, radiate blue, green, yellow and orange after absorbing ultraviolet light.
"This is the first example of an organic that can compete with an organometallic in terms of brightness and color tuning capability," said University of Michigan professor Jinsang Kim.
The novel compounds, called aromatic carbonyls, form strong bonds with halogens in the crystal allowing molecules to be tightly packed, thus suppressing vibration and heat losses during recombination, leading to strong yet tunable phosphorescence. Color is determined by the precise chemical formula, and quantum yields were about 55 percent.
Research associate Kangwon Lee discovered the unique properties of aromatic carbonyls, which was developed further by fellow researcher Onas Bolton. Funding was provided by the National Science Foundation and the National Research Foundation of Korea.
Organic phosphors developed at the University of Michigan could one day lead to cheaper organic light-emitting diodes. Here, they glow in blue and orange when triggered by ultraviolet light. Credit: Marcin Szczepanski, U-M College of Engineering.