Scientists discover the mystery behind gold’s shine

A new study, focusing on thin flakes of monocrystalline gold, has revealed never-before-seen quantum-mechanical effects in photoluminescence that could transform the way solar energy is harnessed and stored.

Carried out by researchers from the École Polytechnique Fédérale de Lausanne (EPFL), the study published in the journal Nature on April 19 involved the creation of gold films of exceptional quality, with thicknesses between 13 and 113 nanometers. By using such precise measurements, the team sought to eliminate confounding variables that undermined previous experiments.

These films were subjected to laser beams and researchers analyzed the subtle glow emitted, which led to unexpected results that required the collaboration of experts in quantum mechanics from several global institutions, including the Barcelona Institute of Science and Technology, the University of Southern Denmark and the Polytechnic Institute of Rensselaer.

International collaborative efforts confirmed that the glow was indeed due to photoluminescencea process influenced by the way holes (the absence of electrons) react to light, in what is the first comprehensive and quantitative model of photoluminescence in gold.

“Using a thin film of monocrystalline gold produced with a new synthesis technique, the team studied the photoluminescence process as the metal became increasingly thinner. We have observed the appearance of certain quantum mechanical effects in films up to 40 nanometerswhich was unexpected, because normally, for a metal, these effects are only seen well below 10 nm”, said Giulia Tagliabue, director of the Nanosciences Laboratory for Energy Technologies (LNET) at EPFL.

The discovery offers new details about where gold’s photoluminescent activity occurs, and could lead to a new method for using the metal itself as a probe in nanoscale temperature measurements.

This ability is critical, as temperature plays a vital role in many chemical reactions on metal surfaces, but measuring it at the nanoscale is notoriously difficult. The team’s findings suggest that gold’s photoluminescent signal could serve as an innovative tool for assessing surface temperatures without biasing the measurement.

“To combat climate change, we will need technologies to convert CO2 into other useful chemicals,” said LNET postdoctoral fellow Alan Bowman, first author of the study, cited by Tech Explorist.

“Using metals is one way to do this, but if we don’t understand how these reactions occur on their surfaces, we can’t optimize them. Luminescence offers a new way of understanding what is happening in these metals”, he concludes.