Experimental benchmarking of dielectric models for simulating the localized surface plasmon resonance in Au-Ag alloy nanospheres

Journal article, 2026

The optical response of gold-silver (Au-Ag) alloy nanoparticles is strongly influenced by their localized surface plasmon resonance (LSPR), which can be tuned by varying the particle composition. Accurate simulation of LSPR, often performed using Mie theory, critically depends on the choice of dielectric function, yet available datasets for gold, silver, and their alloys vary widely. In this work, we aim to demonstrate how different dielectric functions lead to discrepancies in simulated LSPR wavelengths, even for pure metals. By using numerical simulation tools, such as PyMieLab and the miepython library, we systematically evaluate commonly used dielectric models for Au–Ag alloys by comparing their predicted LSPR wavelengths with experimental measurements obtained from spark-ablation-generated nanoparticles with well-defined compositions and narrow size distributions. The composition-dependent experimental LSPR data – obtained for the whole composition range between pure silver and gold – provides a reliable benchmark for assessing the accuracy of each model. Our results highlight the potential uncertainty introduced by different dielectric functions and help to identify a model which describes experimental data the best. The results underline the importance of dielectric model selection for predictive optical simulations of alloy nanoparticles.