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Smart
Optical Materials by Sol-Gel Method
by R.
Reisfeld
Dept.
of Inorganic and Analytical Chemistry
, The
Hebrew University,
Jerusalem 91904, Israel
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Tunable Laser samples prepared by the sol-gel method
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Gasochromic Windows
Optical modulation of WO3 films can be also obtained by UV
or by the introduction of atomic hydrogen (Hº) evolved either from a
HCl/Zn mixture or using Pd spillover (gasochromism). The gasochromic effect, although used in H2 gas sensor applications is obtained by
exposing the WO3 films to atomic hydrogen provided by a thin layer of catalyst (Pt or
Pd) in contact with the film.
The gasochromic switching device is simple and inexpensive because only a single WO3 film covered with a catalyst is sufficient to obtain
colouring/bleaching changes. The original transmittance state of the films can be
recovered by flushing the device with air.
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Gasochromic Palladium doped peroxopolytungstic acid (Pd:P-PTA) films have
been prepared using dip-coating deposition from peroxopolytungstic acid (P-PTA) sols into which PdCl2 was added in molar ratios Pd/W = 1:125, 1:100, 1:53 and 1:40. These films exhibit reversible
coloring/bleaching changes when exposed to hydrogen/argon mixture (4%) and air,
alternatively. Gasochromically colored and bleached films were characterized using in-situ Fourier Transform Infrared (FTIR) spectroscopy.
Coloring/bleaching kinetics of films exposed to H2 and H2/Ar mixture as a function of the concentration of the catalyst and
the temperature of heat treatment has been also reported.
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