Published in “Advanced Science” (Online Publication, January 9, 2024).

For more than 160 years since M. Faraday solved a mystery of vivid ruby-red color of Au colloids, materials that intrinsically exhibit localized surface plasmon resonance (LSPR) in the visible region have been predominantly researched on nanoparticles (NPs) composed of coinage metals, namely Au, Ag, and Cu. In this study, as a coinage metal-free intermetallic NPs, colloidal PtIn₂ NPs with a C1 (CaF₂-type) crystal structure are synthesized by the liquid phase method, which evidently exhibit LSPR in visible region. To investigate the origin of the visible plasmonic nature of C1-PtIn₂ NPs, computational simulations were also conducted. The simulations pointed out differences in the electronic structure and photo-excited electron dynamics between C1-PtIn₂ and face-centered cubic (fcc)-Au NPs; reduced interband transition and stronger screening with smaller number of bound d-electrons compared with fcc-Au are unique origins of the visible plasmonic nature of C1-PtIn₂ NPs.
These results strongly indicate that it is possible to control the plasmonic properties of intermetallic NPs by tuning their crystal structure and composition. Moreover, based on this study, the intermetallic NPs are expected to contribute to the expansion of the library of plasmonic nanomaterials and become an alternative to existing plasmonic materials.

Takekuma, H.; Sato, R.; Iida, K.; Kawawaki, T.; Haruta, M.; Kurata, H.; Nobusada, K.; Teranishi, T., ntrinsic Visible Plasmonic Properties of Colloidal PtIn₂ Intermetallic Nanoparticles, Adv.Sci., DOI : 10.1002/advs.202307055 (2024).