Effect of Al additions on the optical properties of Au α-phase

The effect of aluminium on the optical properties of AlxAu1−x (0 < x < 0.12) substitutional solid solutions is determined. Reflectance spectra and ellipsometric data of a range of compositions are measured and the dielectric functions extracted. Al additions flatten the reflection edge and increase optical loss in the Drude region. The implications of these changes for selected technological applications are investigated. Aluminium is found to be a very effective bleaching agent for Au and could have application for the formulation of improved ‘white gold’ jewellery alloys. However, due to its limited solubility in Au α-phase, other alloying additions would still be required to make a commercially acceptable ‘white gold’. In contrast, the increased optical loss brought by the Al makes the alloys less suitable than pure Au for plasmonic applications or for spectrally selective coatings.