Formation of luminescent silver-clusters and efficient energy transfer to Eu3+ in faujasite NaX zeolite

Faujasite (FAU) type zeolite is built from sodalite cages that joined by oxygen bridges between the hexagonal faces, and is characteristic of high cation exchange capacity and thermal stability. In this research, the FAU-NaX zeolite with Na/Si/Al molar ratio of 4.08:1.4:1.0 was prepared with template-free hydrothermal method and then confirmed with XRD analysis, based on which a series of Ag+ or/and Eu3+ loaded zeolites were obtained through the ion-exchange procedure. The PL spectra measurement indicated that after heat treatment at optimized temperatures between 400-600 degrees C, the Ag+ loaded zeolites showed strong green visible emission centered around 540-550 nm, which is due to the formation of Ag-3(n+) clusters. Furthermore, efficient energy transfer from silverclusters to Eu3+ can be achieved in the Ag (+)/Eu3+ loaded zeolites, and the energy transfer efficiency that evaluated with silver-clusters lifetimes are 23.9%, 44.6%, 67.4% and 73.6%, respectively, in ZX-2Eu30Ag, ZX-5Eu30Ag, ZX-10Eu30Ag and ZX-20Eu30Ag. Besides, the XPS measurements implied that the loading of Eu3+ resulted in a further reduction of silver-clusters, which can also promote the formation of silver-clusters without heat treatment. This new class of metal-clusters and rare earth (RE) ions co-actived phosphors may offer interesting perspective applications in optoelectronics and lighting.