Single Molecule Electroluminescence
Incandescence and luminescence are two main ways of producing light. In incandescence, electric current is passed through a conductor (filament of a light bulb for example). The resistance to the current in the conductor heats it up and it starts emitting light - glowing. Any other form of producing light without heat is called Luminescence, sometimes referred to as 'cold light'. There are various types of luminescence: electroluminescence, chemiluminescence, photoluminescence, etc.
Most glow in the dark toys work on the photoluminescence principle: you expose the dye in the toy to UV - Ultra Violet light (black light) and it emits light in the visible (say green) without getting hot. Emergency light sticks would be an example of chemiluminescence. Two chemicals contained in the stick are mixed when you break the stick and the chemical reaction between them produces light, again without the stick getting hot. Electroluminescence, however, is a phenomenon where electric field energy is converted into light. Plug-in night lights, light emitting diodes, and some displays work on this principle.
Electroluminescent technology has been around for some time; however a research group from the Georgia Institute of Technology has recently made a breakthrough. They produced electroluminescence from a single molecule of silver. They exposed thin films of silver oxide, which are not electroluminescent, to direct current of approximately one ampere. This activated some of the silver oxide molecules, which then appeared within discolored regions in the film (image part A). When electrodes carrying alternating current were then attached to the film a thin line of silver clusters began to emit light in colors that varied depending on the size of the clusters (image part B). When they zoomed in (image part C), single molecule light emission signatures were visible. This was a first observation of a single molecule electroluminescence. Further research may lead to small light sources that can be used on computer chips, small optical memories, high-efficiency quantum information processing and cryptography.
