Light emission from organic materials is not very common in everyday life. However, some living creatures, such as fire flies, emit light with amazingly high efficiencies. In comparison, mass-produced devices such as fluorescent lamps, incandescent light bulbs and television monitors - all of which are based on inorganic materials - are much less efficient. This is partly because organic materials can have extremely high quantum efficiencies for fluorescence - as high as 100% for fire flies. This suggests that organic materials could be used as the basis for a variety of highly efficient light-emitting devices.
Most organic devices, such as displays, emit light by placing the organic material in a very high electric field, a process known as electroluminescence. Light is emitted when these organic molecules - excited into a high energy state by the field - decay to their ground state. The high voltages needed to generate the light (1000 V or more) meant that organic materials did not emerge as realistic candidates for display applications until the development of thin-film devices in the late 1980s.
The first of these devices reached the market in late 1997, and as our understanding of organic materials, light-production mechanisms in these materials and display technology has improved, more organic light-emitting devices have been launched.
In the March issue of Physics World, Junji Kido of Yamagata University, Japan, explains the latest advances in organic displays.