Optical properties of potassium clusters incorporated into zeolite LTA

Abstract

Optical properties are reported for cationic K clusters incorporated into the \ensuremath{\alpha} cage of K-form LTA. The \ensuremath{\alpha} cage has an inside diameter of \ensuremath{\sim}11 \AA{} and is arrayed in a simple cubic structure. The loading density of potassium is systematically changed from dilute to saturated conditions. The average number of guest K atoms is 7.3 per \ensuremath{\alpha} cage at the saturation density. Three groups of absorption and/or reflection bands appear depending on the K loading density. A band at \ensuremath{\sim}2 eV increases and becomes the strongest reflection band with increasing K density, and is assigned to the surface-plasmon-like state of the K cluster. Other groups of bands are relatively weak and are interpreted in terms of the model of the transition between energy bands which originate from 1s, 1p, and 1d molecular orbitals of the K cluster. A Drude-like contribution is found in the analysis of reflection spectra. This is reminiscent of the metallic state of arrayed clusters.