Ultraviolet Exciton-Polaritons in Silver Phenylthiolate

TL;DR

This paper reports the observation of ultraviolet exciton-polaritons in silver phenylthiolate, demonstrating strong light-matter coupling with large Rabi splittings suitable for UV polariton applications.

Contribution

It introduces silver phenylthiolate as a new material platform for UV exciton-polaritons with large Rabi splittings and strong excitonic features in a layered structure.

Findings

UV exciton-polaritons observed with ~500 meV Rabi splitting

Pronounced in-plane excitonic resonance at 3.46 eV with narrow linewidth

High UV birefringence and strong exciton-phonon coupling

Abstract

Ultraviolet (UV) exciton-polaritons (EPs) enable nonlinear optics, polaritonic lasing, and polariton-mediated photochemistry in the short-wavelength regime, yet progress has been limited due to the scarcity of materials that combine large oscillator strength with stable and narrow UV excitons. Here, we demonstrate UV EPs in silver phenylthiolate (Thiorene, AgSPh), a van der Waals (vdW) layered metal-organic chalcogenolate (MOC) that forms a natural multi-quantum-well (MQW) architecture showing strong excitonic features. Imaging spectroscopic ellipsometry reveals a pronounced in-plane excitonic resonance at 3.46 eV with a narrow linewidth of ~ 60 meV, strong UV birefringence ({\Delta}n ~ 0.3), and a high refractive index (n ~ 2.1). Temperature-dependent photoluminescence (PL) shows excitonic emission with a large Stokes shift and substantial exciton-phonon coupling. In both open (self-cavity) and closed cavities, thickness-dependent and angle-resolved reflectance spectra exhibit clear anticrossing, yielding large Rabi splittings of approximately 500 meV. These values are among the largest reported in the UV, positioning thiorene as a promising platform for UV polariton lasers and polariton-enabled photochemistry.