New material promises advances in solid state lighting

"Bright, low power OLEDs are used in some small screens in cell phones or cameras, but at this time, they aren't practical for use in larger displays because of material costs and manufacturing issues," said Kim. "In addition, the OLEDs of today aren't 100% organic, or made of carbon compounds. The organic materials used in them must be spiked with metal to get them to glow." Kim believes this is the first example of an organic material that can compete with an organometallic one in terms of brightness and colour tuning capability. "Purely organic materials have not yet been able to generate meaningful phosphorescence emissions," he said. "The new phosphors exhibit quantum yields of 55%, whereas current pure organic compounds have a yield of essentially zero." Quantum yield, a measure of a material's efficiency and brightness, refers to how much energy an electron dissipates as light instead of heat as it descends from an excited state to a ground state. In Kim's phosphors, the light comes from molecules of oxygen and carbon known as aromatic carbonyls, compounds that produce phosphorescence. "What's unique about these new materials is that the aromatic carbonyls form strong halogen bonds with halogens in the crystal to pack the molecules tightly," explained Kim. "This arrangement suppresses vibration and heat energy losses as the excited electrons fall back to the ground state, leading to strong phosphorescence." Although still in the research stage, Kim believes the material will soon be available commercially for device applications. "The compounds we have created are cheap, easy to synthesise and easy to tune to achieve different colours. We are sure they will bring a big change in the LED and solid state lighting industries," he concluded.