The intermetallic compounds AuAl2 and PtAl2 are colored purple and yellow respectively. In the past they have
been prepared by bulk melting techniques or by co-deposition in a magnetron sputterer. Here, however, we investigate
films of AuAl2, PtAl2 and (Au,Pt)Al2 prepared by sequential physical vapor deposition of the elements,
followed by in situ solid-state reaction. The microstructure, dielectric functions, optical properties and thermal
stability of the resulting films are characterized and compared to those prepared by bulk melting or codeposition.
The (Au,Pt)Al2 films show a color gamut that stretches from purple to brassy yellow depending on
composition and microstructure. High temperature synchrotron X-ray diffraction experiments show that the
(Au,Pt)Al2 phase is metastable, decomposing when heated above 420 °C. In contrast, the pure AuAl2 or PtAl2
phases are stable to about 580 °C before they oxidize or decompose. The alternative possibility of producing
the purple-to-yellow color gamut by depositing optical stacks of very thin films of AuAl2 and PtAl2 is also
assessed. Either scheme will provide a range of colors lying between those of the binary compound endpoints.
Calculations predict that deposition of AuAl2 onto PtAl2 will produce more intense colors than vice versa, an
unexpected finding that is worth further investigation.