| Abstract
| - Silver sulfide clusters are synthesized in the cavities of sodium and calcium zeolite A microcrystals by exposingthe activated Ag+-loaded zeolite to H2S. The growth of the silver sulfide clusters during rehydration of thesamples is investigated by means of diffuse reflectance spectroscopy. Monomers of Ag2S are formed at lowAg+-loading through reaction of AgSH molecules, yielding colorless composites, which exhibit a characteristicblue-green photoluminescence. Yellow colored samples showing an orange-red luminescence with an averagedecay time of 81 μs (−160 °C) are obtained at medium silver sulfide content. Further increasing the silversulfide loading and therefore the cluster size causes a bathochromic shift of this emission which is accompaniedby a shortening of the luminescence lifetime. The samples generally exhibit large Stokes-shifts, which can beattributed to HOMO−LUMO transitions with small oscillator strengths. The Ag2S−zeolite host−guest systemconstitutes a three-dimensional array of silver sulfide clusters. The experimental data and results from quantumchemical calculations suggest that the optical absorption and luminescence properties of this material aremainly due to the presence of isolated silver sulfide clusters inside the zeolite cavities. The characteristics ofthe composites are thereby to a certain extent influenced by the cocations. Most remarkably, strongerluminescence, visible at room temperature, could be observed for silver sulfide clusters in calcium zeolite Acompared to clusters in sodium zeolite A.
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