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Friday, January 29, 1999 Published at 08:57 GMT


Fluorescent lamps go green

The fluorescent lamp is seen virtually everywhere - now even more uses could be possible

The 30-year search for a new kind of luminescent chemical has ended and means it may be possible to make fluorescent lamps more environmentally friendly.

René Wegh explains how the Dutch scientists may have banished mercury
The new material means xenon gas can be used in the bulbs instead of toxic and environmentally-damaging liquid mercury. Also, the xenon does not have to be vapourised so the lamps light instantly.

This means fluorescent lamps, which are more energy efficient, could be used in brake lights, photocopiers and the plasma display screens used for ultra-thin televisions.

Fluorescent lamps light up when an electric current vapourises the liquid mercury in a tube. The energy makes the mercury atoms emit ultra-violet (UV) light which is absorbed by phosphor crystals on the inner walls of the tube. These luminesce, i.e. re-emit the energy as visible light.

The problem with xenon is that the UV light it emits has a shorter wavelength. This is not converted efficiently by conventional phosphors.

[ image: Fluorescent brake lights that light instantly might be possible]
Fluorescent brake lights that light instantly might be possible
But now a team at the Debye Institute, Utrecht University, Holland have solved the problem by managing to squeeze two visible light photons out of one UV photon. They used a combination of elements - europium and gadolinium - to produce a red light.

One of the team, René Wegh, told BBC News Online they were actively searching for similar ways to produce blue and green light. This would enable them to make white light tubes. He expected the work to take at least five years.

The work is published in Science magazine, in which Alok Srivastava, a chemist with General Electric in New York describes the work as very promising: "It is the first experiment to demonstrate that you can get a practical system out of these ideas."

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