Takafumi Miyanaga

By Takafumi Miyanaga, Yushi Suzuki and Sho Narita

In this chapter, studies of structures and optical properties of Ag-zeolite A by means of X-ray absorption fine structure (XAFS) and infrared (IR) spectra are presented. XAFS is a powerful tool to study the local structure of Ag nanoclusters in the zeolite cavity and IR spectra are quite sensitive to the change in zeolite lattice affected by the production of Ag clusters. First, we focus on the creation of Ag clusters in zeolite A by heat treatment under atmosphere and vacuum. Second, we discuss the mechanism of photoluminescence for Ag-zeolite composite. It is widely believed that the emitting point is Ag clusters in the Ag zeolite; on the other hand, our recent result is contradicted that Ag clusters are broken down in the strongly emitting species.

Part of the book: Zeolites

By Yushi Suzuki, Takafumi Miyanaga, Kazuma Yamauchi, Saya Okita, Yoshiki Oka and Reki Nakamura

We use operando X-ray absorption fine structure (XAFS) to analyze the relation between the properties of photoluminescence (PL) and the structures of Ag clusters and Ag ions. The Ag clusters are generated by evacuation in the cavity of Ag-type zeolite-X. The Ag clusters in the zeolite cavity collapse when exposed to the atmosphere. The results reported herein indicate that the collapsing Ag cluster plays an important role in generating strong PL bands and that Ag clusters might not be a direct species of PL. Results of XAFS analysis show that the Ag cluster formed in the zeolite cavity by evacuation can be tetrahedral with four atoms. By evacuation, 9 or 10 Ag tetrahedral are formed, two of which are expected to be responsible for strong PL. This result suggests that the Ag ion position after cluster collapse plays an important role in PL band generation and that Ag clusters are not direct luminescent species of PL.

Part of the book: Mineralogy