Quantum-mechanical effects in photoluminescence from thin crystalline gold films

TL;DR

This study uncovers quantum-mechanical effects in the photoluminescence of thin crystalline gold films, revealing how film thickness influences luminescence through electronic band structure discreteness, supported by experiments and first-principles simulations.

Contribution

It provides the first experimental and theoretical evidence of quantum effects in gold luminescence, linking film thickness to electronic structure modifications.

Findings

Quantum effects are observable in gold flakes up to 40 nm thick.

Luminescence changes are due to out-of-plane electronic band structure discreteness.

First-principles models qualitatively reproduce experimental observations.

Abstract

Luminescence constitutes a unique source of insight into hot carrier processes in metals, including those in plasmonic nanostructures used for sensing and energy applications. However, being weak in nature, metal luminescence remains poorly understood, its microscopic origin strongly debated, and its potential for unravelling nanoscale carrier dynamics largely unexploited. Here, we reveal quantum-mechanical effects emanating in the luminescence from thin monocrystalline gold flakes. Specifically, we present experimental evidence, supported by first-principles simulations, to demonstrate its photoluminescence origin when exciting in the interband regime. Our model allows us to identify changes to the measured gold luminescence due to quantum-mechanical effects as the gold film thickness is reduced. Excitingly, such effects are observable in the luminescence signal from flakes up to 40 nm in thickness, associated with the out-of-plane discreteness of the electronic band structure near the Fermi level. We qualitatively reproduce the observations with first-principles modelling, thus establishing a unified description of luminescence in gold and enabling its widespread application as a probe of carrier dynamics and light-matter interactions in this material. Our study paves the way for future explorations of hot-carriers and charge-transfer dynamics in a multitude of material systems.