Representative studies have been reported where the use of silver-zeolites of silversulfur-zeolites has rendered into the fabrication of white-emissive LED prototypes
[77, 79]. We might be witnesses, in a very close future, of the first generation of light
emitting devices based on silver-exchanged zeolite phosphors, which could represent a breakthrough toward the gradual replacement of lanthanide-based phosphors
in light emitting devices.
4.2 Humidity Sensors
The ability of Ag clusters confined in zeolites to optically respond to external stimuli
can be utilized in sensing applications. For instance, several reports have suggested
the use of silver-zeolites as vapor sensors based on their absorption response to
hydration levels [114], leading to samples with different colors depending on their
water content. The luminescence response of silver-zeolites toward the presence of
water has been also observed [102]. Where the exposure of silver-zeolite samples to
high-humidity environments led to a quenching of the luminescence. This process
was demonstrated to be fully reversible and a subsequent drying step by mild heating
showed the reestablishment of their original luminescent properties. Up to now the
sensing characteristics of silver clusters confined in zeolites were based on a
“positive or negative” response using the depletion/activation of their luminescence
properties. However, in a recent study, the dynamic emission color change of silver
clusters stabilized in LTA (containing lithium as counter balancing ion) zeolites with
respect to their hydration level was shown (Fig. 7) [70]. This major improvement in
the stimuli-to-response process could have direct implications in the use of these
materials as luminescence-based humidity sensors at macro and micro scale.
Fig. 6 Silver-zeolite-based phosphors and lanthanide-based commercial phosphors under 254 nm
illumination (left). Working fluorescent lamp prototype using green-emitting silver-zeolite phosphor materials (right)
Highly Luminescent Metal Clusters Confined in Zeolites
95
[77, 79]. We might be witnesses, in a very close future, of the first generation of light
emitting devices based on silver-exchanged zeolite phosphors, which could represent a breakthrough toward the gradual replacement of lanthanide-based phosphors
in light emitting devices.
4.2 Humidity Sensors
The ability of Ag clusters confined in zeolites to optically respond to external stimuli
can be utilized in sensing applications. For instance, several reports have suggested
the use of silver-zeolites as vapor sensors based on their absorption response to
hydration levels [114], leading to samples with different colors depending on their
water content. The luminescence response of silver-zeolites toward the presence of
water has been also observed [102]. Where the exposure of silver-zeolite samples to
high-humidity environments led to a quenching of the luminescence. This process
was demonstrated to be fully reversible and a subsequent drying step by mild heating
showed the reestablishment of their original luminescent properties. Up to now the
sensing characteristics of silver clusters confined in zeolites were based on a
“positive or negative” response using the depletion/activation of their luminescence
properties. However, in a recent study, the dynamic emission color change of silver
clusters stabilized in LTA (containing lithium as counter balancing ion) zeolites with
respect to their hydration level was shown (Fig. 7) [70]. This major improvement in
the stimuli-to-response process could have direct implications in the use of these
materials as luminescence-based humidity sensors at macro and micro scale.
Fig. 6 Silver-zeolite-based phosphors and lanthanide-based commercial phosphors under 254 nm
illumination (left). Working fluorescent lamp prototype using green-emitting silver-zeolite phosphor materials (right)
Highly Luminescent Metal Clusters Confined in Zeolites
95