Plastics that emit light

Television screens that can be rolled up for transport or storage, wallpapers and clothes whose pattern can be changed at will and faster internet connections are being developed by university researchers.

Professor Ifor Samuel of St Andrews University, Scotland, and Dr P L Burn, Professor at Oxford University, UK, have discovered light-emitting materials based on snowflake-like molecules that allow colour properties to be controlled.

Nearly all plastics are electrical insulators but a type known as conjugated polymers can carry an electric current. ''Conjugated refers to the different structure enabling materials to transmit electricity. In fact, they are electrical semiconductors and provide a new class of materials for electronics and photonics,'' said Professor Samuel.

''Traditional semiconductors are rigid crystalline materials like silicon. Plastic semiconductors are exciting because they combine the useful electronic properties of semiconductors with the advantages of plastics making them easy to shape and simple to manufacture. In addition, the structure of plastic can be changed to tune properties such as the colour of the material."

''A whole range of semiconductor devices can be made: transistors for simple circuits, light-emitting diodes that display information, solar cells and even lasers. Because they are made from plastic, these devices have remarkable new properties such as being flexible. When a voltage is applied to a thin layer of semiconducting polymer, light is emitted. This provides the basis for the new display technologies,'' he added.

Molecules of the light-emitting material are dendritic (shaped like a snowflake) and known as dendrimers. The researchers have optimised the electronic and optical properties to make red, green and blue light-emitting dendrimers required for colour display.

''In addition to information displays in applications such as personal organisers, they will be suitable for making light-emitting wallpaper or clothing. The discovery also has many other applications which we are exploring,'' said Professor Samuel.

University of St Andrews website