dynamical formation of trimers and hexamers Ag clusters in silver-exchanged
zeolites was proposed depending on the silver content. The formation of trimer Ag
species was observed in samples having low silver loadings, whereas the appearance
of the hexamer Ag clusters was attributed to the interaction of two trimer species
within the sodalite cages of silver-exchanged LTA zeolites containing higher silver
loadings. ESR has been mainly applied to obtain information related to the behavior
of silver clusters in zeolites during catalytic reactions. Nevertheless, in a recent
report, the use of ESR as a tool to elucidate the electronic properties of luminescent
silver-exchanged LTA samples was demonstrated [19]. In this work, the presence of
partially reduced paramagnetic Ag 6
+ silver clusters in Ag-LTA samples was associated with the red emission observed in this particular sample.
TGA is an auxiliary technique utilized to investigate the water content at different
temperatures in silver-exchanged zeolites [102]. The results obtained by this technique have contributed to the analysis of the relationship between silver clusters and
their environment (ligands). For instance, based on X-ray diffraction and TGA
evidence, the debate about the electrons source involved in the synthesis of thermally
auto-reduced silver clusters in zeolites was clarified [19].
Although several characterization techniques employed in the study of silver
clusters confined in zeolite matrices have been discussed in the previous sections,
there is no a universal technique to deal with this task, a more combinatorial
approach is needed to decipher the physicochemical properties and formation
mechanisms of such small metal entities. The use of a particular technique above
others is determined by the approach employed and the information required. Most
of the above revised characterization techniques have been used to try to correlate
the structure-to-luminescence properties relationship of silver-exchanged zeolites
and establish the basis of more rational design and synthesis of multifunctional silver
clusters in zeolite matrices.
4 Applications of Luminescent Silver-Containing Zeolites
4.1 Phosphors for Lighting Applications
Luminescent silver-zeolite composites display interesting emissive properties, such
as large Stokes shifts, high external quantum efficiencies, and large photostability,
among others. Depending on the zeolite topology, the presence of specific counter
balancing ions, and the silver loading, different emissive silver species can be
created upon thermal treatment, with spectral properties ranging from blue to red.
Therefore, this new class of photostable luminescent materials with tunable emission
colors offers interesting perspectives as wavelength converters in fluorescent lamps
and LEDs (Fig. 6). To date, several publications and patents have demonstrated the
high applicability of these versatile materials to be implemented in light emitting
devices [19, 27, 73, 111–113]. Recent efforts have been directed to the synthesis of
single-phase white emitting phosphors with absorption in the NUV region.
94
E. Coutino-Gonzalez et al.
zeolites was proposed depending on the silver content. The formation of trimer Ag
species was observed in samples having low silver loadings, whereas the appearance
of the hexamer Ag clusters was attributed to the interaction of two trimer species
within the sodalite cages of silver-exchanged LTA zeolites containing higher silver
loadings. ESR has been mainly applied to obtain information related to the behavior
of silver clusters in zeolites during catalytic reactions. Nevertheless, in a recent
report, the use of ESR as a tool to elucidate the electronic properties of luminescent
silver-exchanged LTA samples was demonstrated [19]. In this work, the presence of
partially reduced paramagnetic Ag 6
+ silver clusters in Ag-LTA samples was associated with the red emission observed in this particular sample.
TGA is an auxiliary technique utilized to investigate the water content at different
temperatures in silver-exchanged zeolites [102]. The results obtained by this technique have contributed to the analysis of the relationship between silver clusters and
their environment (ligands). For instance, based on X-ray diffraction and TGA
evidence, the debate about the electrons source involved in the synthesis of thermally
auto-reduced silver clusters in zeolites was clarified [19].
Although several characterization techniques employed in the study of silver
clusters confined in zeolite matrices have been discussed in the previous sections,
there is no a universal technique to deal with this task, a more combinatorial
approach is needed to decipher the physicochemical properties and formation
mechanisms of such small metal entities. The use of a particular technique above
others is determined by the approach employed and the information required. Most
of the above revised characterization techniques have been used to try to correlate
the structure-to-luminescence properties relationship of silver-exchanged zeolites
and establish the basis of more rational design and synthesis of multifunctional silver
clusters in zeolite matrices.
4 Applications of Luminescent Silver-Containing Zeolites
4.1 Phosphors for Lighting Applications
Luminescent silver-zeolite composites display interesting emissive properties, such
as large Stokes shifts, high external quantum efficiencies, and large photostability,
among others. Depending on the zeolite topology, the presence of specific counter
balancing ions, and the silver loading, different emissive silver species can be
created upon thermal treatment, with spectral properties ranging from blue to red.
Therefore, this new class of photostable luminescent materials with tunable emission
colors offers interesting perspectives as wavelength converters in fluorescent lamps
and LEDs (Fig. 6). To date, several publications and patents have demonstrated the
high applicability of these versatile materials to be implemented in light emitting
devices [19, 27, 73, 111–113]. Recent efforts have been directed to the synthesis of
single-phase white emitting phosphors with absorption in the NUV region.
94
E. Coutino-Gonzalez et al.