Scientists create jewel-toned organic phosphorescent crystals

LONDON - University of Michigan researchers have created a new class of material that shines with phosphorescence, which they say could lead to cheaper, more efficient and flexible display screens, among other applications.

Jinsang Kim and his colleagues made metal-free organic crystals that are white in visible light and radiate blue, green, yellow and orange when triggered by ultraviolet light.

By changing the materials’ chemical composition, the researchers can make them emit different colours.

The light comes from molecules of oxygen and carbon known as “aromatic carbonyls,” compounds that produce phosphorescence, but weakly and under special circumstances such as extremely low temperatures.

And the aromatic carbonyls form strong halogen bonds with halogens in the crystal to pack the molecules tightly. This arrangement suppresses vibration and heat energy losses as the excited electrons fall back to the ground state, leading to strong phosphorescence.

The OLEDs of today aren’t 100 percent organic, or made of carbon compounds. The organic materials used in them must be spiked with metal to get them to glow.

“Purely organic materials haven’t been able to generate meaningful phosphorescence emissions. We believe this is the first example of an organic that can compete with an organometallic in terms of brightness and color tuning capability,” said Kim.

The new phosphors exhibit “quantum yields” of 55 percent.

These new compounds can bring the price down even further, because they don’t require precious metals. They’re made primarily of inexpensive carbon, oxygen, chlorine and bromine.

“This is in the beginning stage, but we expect that it will not be long before our simple materials will be available commercially for device applications,” Kim said.

“And we expect they will bring a big change in the LED and solid-state lighting industries because our compounds are very cheap and easy to synthesize and tune the chemical structure to achieve different colors and properties.”

The study appears in Nature Chemistry. (ANI)