Organic light-emitting diodes (OLEDs) are a technology that shows great promise, as they are thinner, lighter, and less expensive to manufacture than their non-organic LED counterparts. Despite their name, however, they are not fully organic, as small amounts of precious metals are required to make them glow. A completely organic and even cheaper alternative could be on its way, though ... researchers from the University of Michigan have created metal-free organic crystals that shine with phosphorescence – until now, only non- or semi-organic compounds have displayed this property.
The crystals – or phosphors – glow white in visible light, while radiating blue, green, yellow and orange in ultraviolet light. Different colors can be obtained by altering their chemical composition.
The light itself comes from molecules of oxygen and carbon called “aromatic carbonyls.” Typically, they only produce a weak phosphorescence, and only under special conditions such as very low temperatures. In the U Michigan material, however, the carbonyls bond with halogens in the crystal, packing the molecules tightly. This suppresses vibration, minimizing energy lost as heat, and maximizing energy that produces phosphorescence under practical conditions. The result is a brightness comparable to that of OLEDs, which are themselves brighter than LEDs.
“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,” said lead researcher Jinsang Kim. “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 university is currently looking into patenting the technology, and seeking partners for commercialization.
The research was recently published in the journal Nature Chemistry.