Theoretical modeling of optical properties of Ag8 and Ag14 silver clusters embedded in an LTA sodalite zeolite cavity

Abstract

Optical properties of silver Ag_n nanoclusters are demonstrated to be dependent on their size, structure and charge state. It is found that when being contained in the sodalite cavity of LTA zeolite the tetradecanuclear hexacation silver cluster Ag₁₄⁶⁺ is stable. Its lower-lying states and optical spectrum are theoretically determined using the quantum chemical TD-DFT method. Its ground state possesses an outer-shell electron configuration of A_1g²T_2g⁶ mimicking the s²p⁶ valence of noble gas atoms. These frontier orbitals are constructed from 5s,5p(Ag)-AOs with contributions from framework oxygen atoms. Light absorption of Ag₁₄⁶⁺ embedded in the sodalite cage which is characterized by strong peaks centered at 331 and 476 nm (transitions 5s,p(Ag) → 5s,p(Ag)) leads to much longer wavelength emission. The sodalite cage, as a container, stabilizes the central Ag₁₄⁶⁺ cluster by electrostatic attraction. The absorption spectrum of the isovalent neutral Ag₈ cluster embedded inside the same sodalite cavity is also simulated using TD-DFT and CASPT2 methods. This absorption spectrum which is similar to that of the Ag₁₄⁶⁺ cluster has two absorption bands in the near UV and visible regions.