Optical Absorption of Aluminum Nanoparticles

Abstract

In this study, the optical absorption properties of small Aluminum (Al) nanoparticles were systematically investigated by using Density Functional Theory (DFT) calculations. A series of nanostructures ranging from Al₄ to Al₂₄ was modeled and optimized using the Perdew, Burke, and Ernzerhof (PBE0) functional and def2-TZVP basis set. The resulting absorption spectra revealed that both the position and intensity of the first and highest absorption peaks depend strongly on the size and geometry of the clusters. A gradual redshift of the first absorption peak was observed as the number of atoms increased, transitioning from the Ultraviolet (UV) to the visible and eventually to the Near-Infrared (NIR) region of the electromagnetic spectrum. The Al₅ cluster exhibited the most favorable first peak in the UV region, which was calculated at 3.90 eV, Al₈ in the visible, which was calculated at 2.47 eV, and Al₁₂ in the NIR, calculated at 1.51 eV. Similarly, the highest absorption peak transitioned from the UV for Al₄, calculated at 4.66 eV, to the visible region for Al₁₃, which was found at 2.83 eV with increasing cluster size. The binding energy calculations indicated increasing structural stability with size, peaking at 2.70 eV for the Al₂₃ cluster. These findings confirm the high tunability of the optical properties of Al nanoclusters and underscore their potential in plasmonic applications across the Ultraviolet Visible (UV-Vis)-NIR spectrum. Given aluminum’s low cost, abundance, and strong light-matter interaction, this group of nanoparticles emerges as a promising alternative to noble metals and copper for a wide range of nanophotonic and plasmonic technologies.