Ab initio calculation of stressed cesium iodide lattices and resulting surface plasmon resonance peak shifts

Abstract

Alkali halides have received attention due to their potential application as detector coating. This is due to the appearance of Surface Plasmon Resonance (SPR) absorption peaks in their absorption spectrum. The formation of SPR peaks is due to the formation of cesium metal clusters within the cesium halide matrix. Experimental work on cesium iodide explained the formation of cesium clusters in cesium iodide films. It was experimentally seen that when iodine atom escapes from the cesium iodide unit cell, then the newly created cubic unit cell of cesium exerts force on neighboring cesium iodide unit cells. This force results in cesium iodide taking up a tetragonal lattice structure. The aim of this paper is to theoretically investigate the tetragonal cesium iodide’s band structure and dielectric constant using ab initio calculations. The results indicate that both the band structure and the dielectric constant of cesium iodide in tetragonal phase show a systematic variation with changes in the lattice constant. This alteration in dielectric constant or variation in refractive index of cesium iodide, which acts as the surrounding media for the cesium metal clusters, induces a shift in the SPR peak position. The calculated dielectric constants were used for Gan model calculations of the extinction coefficient and evaluation of SPR peak position ([Formula: see text]). A redshift in [Formula: see text] was seen with increasing dielectric constant that appears with stress acting on cesium iodide’s lattice. These results were found to be in agreement with experimental results reported earlier by us.