Optical Properties of Noncubic Au Microcrystallites

The optical properties of anisotropic Au crystallites are governed by their size, shape, and crystal structure. However, the influence of crystallinity on the optical properties of Au crystallites is much unexplored. Recently, bipyramidal Au crystallites hosting noncubic lattices, body-centred orthorhombic and body centred tetragonal (together named as bc(o,t) ) have been synthesized in the laboratory. These crystallites exhibit extraordinary catalytic performance and are robust at pressures up to ∼40 GPa and temperatures of 700 °C. In this study, we have investigated the extinction properties of the Au microcrystallites while varying the noncubic mole fractions by carefully tuning the synthetic conditions. The crystallites show near-infrared plasmonic features associated with multipolar resonances. The experimental observations have been compared with calculations performed using the discrete dipolar approximation (DDA) method. While there is a reasonable agreement between the two, the noncubic nature of the lattice seems to have little influence on the optical properties investigated. The obtained results strengthen the proposed core-shell (fcc shell, capped bc(o,t) core) morphology of Au crystallites.