Cascade Brillouin scattering as a mechanism for photoluminescence from rough surfaces of noble metals

TL;DR

This paper introduces a theory explaining photoluminescence in noble metal surfaces as cascade Brillouin scattering, unifying high- and low-frequency spectral features observed in surface-enhanced Raman experiments.

Contribution

It presents a novel theoretical framework linking photoluminescence to cascade Brillouin scattering by metal phonons, explaining experimental spectral features.

Findings

The theory matches experimental spectra across the entire frequency range.

Photoluminescence arises from cascade Brillouin scattering under plasmon resonance.

The model unifies high- and low-frequency spectral observations.

Abstract

In surface-enhanced Raman scattering experiments that use plasmonic nanostructures as substrates, the scattering spectrum contains a broad background usually associated with photoluminescence. This background exists above and below the frequency of the incident wave. The low-frequency part of this background is similar to the scattering spectrum of a plasmon nanoparticle, while the high-frequency part follows the Gibbs distribution. We develop a theory that explains experimentally observed features in both the high- and low-frequency parts of the photoluminescence spectrum from a unified point of view. We show that photoluminescence is attributed to the cascade Brillouin scattering of the incident wave by metal phonons under the plasmon resonance conditions. The theory is in good agreement with our measurements over the entire frequency range of the background.