induced strengthening of the interaction between the fluorenone carbonyl group and
the ZL potassium cations, thus indicating a way to the realization of, e.g., optical
devices able to maintain their functionality under extreme conditions [49]. The high
baric stability of the ZL framework was confirmed in a compressibility behavior and
pressure-induced over-hydration study [161].
7 Electronic Absorption and Luminescence Properties
of the Host-Guest Composites
The electronic properties of the guests are influenced by interactions with the host,
with the charge compensating cations, with co-guests, by interactions between the
guests, and by the spatial restrictions imposed by the host. It is important to
distinguish between the influence of such interactions on spectroscopic data and
the frequently present influences of physical effects such as light-scattering, lightguiding, and self-absorption which is usually followed by re-emission, in order to
avoid misinterpretation. Pure ZL crystals do not show any electronic absorption in
the visible and in the near UV up to about 200 nm or even 180 nm. The weak
vibration overtone absorption present in the near IR must be considered in near IR
absorption and luminescence spectroscopy. Diffuse reflectance techniques are popular for measuring electronic absorption and luminescence spectra. Measurements
on very thin layers covered by a refractive index matching polymer or oil allow
analyzing and, if desired, suppressing intra-particle effects such as self-absorption,
saturation of single particles of samples with high loading, or wave-guiding processes. These processes may affect considerably the shape of the spectra, the
luminescence quantum yields, and luminescence decay [20, 46, 169–172]. The
influence of extra- and intra-particle self-absorption and re-emissions on the shape
of the spectra and the luminescence quantum yield has been discussed in detail
[171]. These effects do not concern the luminescence properties of rare earth-ZL
composites because for them self-absorption is usually negligible. The nature of the
cations that must compensate 3.6 negative charges per u.c. is of considerable
importance. Their impact depends on the type and concentration of the co-solvent
which has been water in most cases investigated so far. Little is known regarding the
influence of organic co-guests such as n-octane and similar. The heavy atom effect
[173], which enhances singlet to triplet intersystem crossing and thus triplet emission, was studied by Ramamurthy et al. The authors compared the influence of alkali
cations and of Tl
+ on the phosphorescence yield of naphthalene and related aromatic
guest in zeolite X and Y. They observed a decrease of S 0
S 1 emission accompanied with an increase of the phosphorescence yield in the following order:
Li
+
% Na
+
% K
+
< Rb
+
< Cs
+
<< Tl
+ [174, 175]. This corroborates with the Z
4
increase of the efficiency of spin-orbit coupling with the atomic number Z
[176]. Similar studies for ZL are missing. It seems, however, reasonable to assume
that a basically similar heavy atom effect should apply. Hashimoto et al. observed
Guests in Nanochannels of Zeolite L
33
the ZL potassium cations, thus indicating a way to the realization of, e.g., optical
devices able to maintain their functionality under extreme conditions [49]. The high
baric stability of the ZL framework was confirmed in a compressibility behavior and
pressure-induced over-hydration study [161].
7 Electronic Absorption and Luminescence Properties
of the Host-Guest Composites
The electronic properties of the guests are influenced by interactions with the host,
with the charge compensating cations, with co-guests, by interactions between the
guests, and by the spatial restrictions imposed by the host. It is important to
distinguish between the influence of such interactions on spectroscopic data and
the frequently present influences of physical effects such as light-scattering, lightguiding, and self-absorption which is usually followed by re-emission, in order to
avoid misinterpretation. Pure ZL crystals do not show any electronic absorption in
the visible and in the near UV up to about 200 nm or even 180 nm. The weak
vibration overtone absorption present in the near IR must be considered in near IR
absorption and luminescence spectroscopy. Diffuse reflectance techniques are popular for measuring electronic absorption and luminescence spectra. Measurements
on very thin layers covered by a refractive index matching polymer or oil allow
analyzing and, if desired, suppressing intra-particle effects such as self-absorption,
saturation of single particles of samples with high loading, or wave-guiding processes. These processes may affect considerably the shape of the spectra, the
luminescence quantum yields, and luminescence decay [20, 46, 169–172]. The
influence of extra- and intra-particle self-absorption and re-emissions on the shape
of the spectra and the luminescence quantum yield has been discussed in detail
[171]. These effects do not concern the luminescence properties of rare earth-ZL
composites because for them self-absorption is usually negligible. The nature of the
cations that must compensate 3.6 negative charges per u.c. is of considerable
importance. Their impact depends on the type and concentration of the co-solvent
which has been water in most cases investigated so far. Little is known regarding the
influence of organic co-guests such as n-octane and similar. The heavy atom effect
[173], which enhances singlet to triplet intersystem crossing and thus triplet emission, was studied by Ramamurthy et al. The authors compared the influence of alkali
cations and of Tl
+ on the phosphorescence yield of naphthalene and related aromatic
guest in zeolite X and Y. They observed a decrease of S 0
S 1 emission accompanied with an increase of the phosphorescence yield in the following order:
Li
+
% Na
+
% K
+
< Rb
+
< Cs
+
<< Tl
+ [174, 175]. This corroborates with the Z
4
increase of the efficiency of spin-orbit coupling with the atomic number Z
[176]. Similar studies for ZL are missing. It seems, however, reasonable to assume
that a basically similar heavy atom effect should apply. Hashimoto et al. observed
Guests in Nanochannels of Zeolite L
33