 Press Release
Angew. Chem. Int. Ed. 2002,
41 (13), 2284 - 2288
No. 13/2002
New Building Blocks for Optronics/Photonics
Dye-filled zeolith
minicrystals
for the capture and storage of light energy
Plant photosynthesis, the conversion of light into (bio)chemical
energy, is endlessly fascinating. Just as a radio uses an antenna to absorb
electromagnetic waves from the atmosphere, plants use their chlorophyll
to capture certain wavelengths of visible light and pass the light's
energy on to their photosynthetic apparatus. Such "photonic
antennas" would also be great for technical applications,
particularly for a new, more highly efficient generation of solar
cells.
A research group at the University of Bern has now attained
extremely promising results with their artificial photonic antenna; in
order to capture light, Gion Calzaferri and Huub Maas are using
molecules of a green fluorescent dye, which they have introduced into
the linear channels in tiny, porous, zeolite crystals. When the
fluorescent dye is irradiated, the molecules absorb quanta of light.
With the help of these "packets of energy", the electrons of
the dye can jump into an excited state - much like a different
"orbit". After a short time, the electrons fall back to their
original orbit. A small portion of the energy released in this process
is dispersed as vibrations throughout the molecules. The rest of the
energy is released as another quantum of light. Because this quantum
has less energy than was originally absorbed, its color is different.
This phenomenon is known as fluorescence. When the dye molecules are
stuck into the channels that cross through the crystals parallel to
their long axes, they are neatly packed right up against each other.
This allows them to pass the packets of energy directly - without
conversion into light - from molecule to molecule. The special twist is
this: the Swiss researchers plugged up the openings of the channels
with a second type of fluorescent dye. The two types of molecules are
precisely tuned to each other; the "plugs" are thus also able
to accept energy packets from the electronic excitation, but they are
not able to pass them back to the "emitters" within the
crystal. The "plugs" re-emit the energy as red fluorescence
on the surface of the little crystals - where it can be recaptured.
This "receiving antenna" can alternatively be made into a
"transmitter" if the two fluorescent dyes are more or less
switched. The "plugs" capture energy from outside, which they
then pass on to the molecules inside the crystals. These then
fluoresce, which is useful for making such things as new light emitting
diodes.
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