On the origin of blueshifts in organic polariton condensates

TL;DR

This paper investigates the causes of energy-shifts in organic polariton condensates, revealing that they originate from molecular transition saturation and energy migration, contrasting with inorganic systems.

Contribution

It introduces a model explaining blueshifts in organic polariton condensates based on molecular saturation and energy migration, differing from inorganic exciton interactions.

Findings

Blueshifts are due to molecular transition saturation and energy migration.

The model predicts step-wise increases in emission energy and polarization at threshold.

Interparticle Coulomb exchange is negligible in organic systems.

Abstract

We report on the origin of energy-shifts in organic polariton condensates. The localised nature of Frenkel excitons in molecular semiconductors precludes interparticle Coulomb exchange interactions -the latter being the dominant mechanism for blueshifts in inorganic semiconductor microcavities that bear Wannier-Mott excitons. We examine the contribution of optically induced change of the intracavity non-linear refractive index, gain induced frequency-pulling and quenching of the Rabi splitting, as well as the role of polariton-exciton and polariton-polariton scattering in the energy-shift of the polariton mode at condensation threshold in strongly coupled molecular dye microcavities. We conclude that blueshifts in organic polariton condensates arise from the interplay of the saturation of molecular optical transitions and intermolecular energy migration. Our model predicts the commonly observed step-wise increase of both the emission energy and degree of linear polarisation at polariton condensation threshold.