Absorption and Photoluminescence in Organic Cavity QED

TL;DR

This paper introduces a theoretical framework for understanding spectroscopic signals in organic microcavities, revealing dark vibronic polaritons and explaining photoluminescence phenomena through a Holstein-Tavis-Cummings model with dissipation.

Contribution

It develops a novel theoretical approach to interpret complex spectroscopic features in organic cavity QED, including dark vibronic polaritons and emission enhancements, aligning well with experimental data.

Findings

Identification of dark vibronic polaritons as non-absorbing yet emissive states.

Explanation of photoluminescence enhancement via photon leakage from dark states.

Clarification of the apparent absorption-emission reciprocity breakdown.

Abstract

Organic microcavities can be engineered to reach exotic quantum regimes of strong and ultrastrong light-matter coupling. However, the microscopic interpretation of their spectroscopic signals can be challenging due to the competition between coherent and dissipative processes involving electrons, vibrations and cavity photons. We develop here a theoretical framework based on the Holstein-Tavis-Cummings model and a Markovian treatment of dissipation to account for previously unexplained spectroscopic features of organic microcavities consistently. We identify conditions for the formation of dark vibronic polaritons, a new class of light-matter excitations that are not visible in absorption but lead to strong photoluminescence lines. We show that photon leakage from dark vibronic polaritons can be responsible for enhancing photoluminescence at the lower polariton frequency, and also explain the apparent breakdown of reciprocity between absorption and emission in the vicinity of the bare molecular transition frequency. Successful comparison with experimental data demonstrates the applicability of our theory.