the two substrates is explained by the diffusion of silver into the soda-lime glass
substrate, this process being based on an exchange between Ag
þ ions in the coating
and Na
þ ions of the substrate. In the coatings on silica carriers, silver is always
present as Ag
0 (metallic silver); annealing of the specimen with soda-lime glass
substrates above 523 K leads to a reduction of the Ag
þ ions by the precipitation of
silver nanoparticles, which show no photoluminescence.
9.6
Special Luminescent Nanocomposites
Various specialized applications exist where the use of semiconducting quantum
dots based on, for example, cadmium, selenium, or tellurium, is not desirable due to
potential problems of toxicity and carcinogenicity. Furthermore, most luminescent
compounds made from these elements have only a limited stability against oxidation
and hydrolysis. On occasion, such problems make the handling – and therefore also
the application – of these materials extremely difficult and this has led to a search for
luminescent oxide nanoparticles comprised of nontoxic constituents that are stable
in water.
One possible way in which these problems might be overcome would be to dope
the oxide nanoparticles with small amounts of rare earth ions. Figure 9.41 displays
two examples of nanocrystalline zirconia doped with dysprosium and europium.
Doping of oxides with small amounts of rear earth elements gives a broad range of
possible luminescent particles. The main advantage of this approach may be seen in
the high stability of these particles. Additionally, using zirconia as basic material
keeps the prices in reasonable ranges.
A completely new approach [12,18] of overcoming the above-described problems
is to use insulating oxide nanoparticles coated with a polymer. Although the
Figure 9.40 Photoluminescence spectra of silver-doped silica films on soda lime glass substrate
as a function of annealing temperature according to García et al. [33].
9.6 Special Luminescent Nanocomposites j243
substrate, this process being based on an exchange between Ag
þ ions in the coating
and Na
þ ions of the substrate. In the coatings on silica carriers, silver is always
present as Ag
0 (metallic silver); annealing of the specimen with soda-lime glass
substrates above 523 K leads to a reduction of the Ag
þ ions by the precipitation of
silver nanoparticles, which show no photoluminescence.
9.6
Special Luminescent Nanocomposites
Various specialized applications exist where the use of semiconducting quantum
dots based on, for example, cadmium, selenium, or tellurium, is not desirable due to
potential problems of toxicity and carcinogenicity. Furthermore, most luminescent
compounds made from these elements have only a limited stability against oxidation
and hydrolysis. On occasion, such problems make the handling – and therefore also
the application – of these materials extremely difficult and this has led to a search for
luminescent oxide nanoparticles comprised of nontoxic constituents that are stable
in water.
One possible way in which these problems might be overcome would be to dope
the oxide nanoparticles with small amounts of rare earth ions. Figure 9.41 displays
two examples of nanocrystalline zirconia doped with dysprosium and europium.
Doping of oxides with small amounts of rear earth elements gives a broad range of
possible luminescent particles. The main advantage of this approach may be seen in
the high stability of these particles. Additionally, using zirconia as basic material
keeps the prices in reasonable ranges.
A completely new approach [12,18] of overcoming the above-described problems
is to use insulating oxide nanoparticles coated with a polymer. Although the
Figure 9.40 Photoluminescence spectra of silver-doped silica films on soda lime glass substrate
as a function of annealing temperature according to García et al. [33].
9.6 Special Luminescent Nanocomposites j243