AuAl2 and PtAl2 as potential plasmonic materials

•The electronic structure dielectric functions of PtAl2, AuAl2 and intermediate alloys were calculated.•The experimental reflectivity and EELS for PtAl2 showed good agreement with the theoretical spectra.•The yellow color of PtAl2 is associated with a bulk plasmon at 3eV.•These materials are good candidates for applications in plasmonics.