# Phonon-assisted Photoluminescence from Dark Excitons in Monolayers of Transition Metal Dichalcogenides

## TL;DR

This paper develops a microscopic theory to explain phonon-assisted photoluminescence from dark excitons in transition metal dichalcogenides, clarifying emission features below the bright exciton line in tungsten and molybdenum-based materials.

## Contribution

It introduces a comprehensive microscopic model for phonon-assisted dark exciton recombination, explaining experimental PL spectra in TMD monolayers.

## Key findings

- WSe₂ shows visible low-temperature PL from dark exciton recombination.
- Different configurations of bright and dark states explain spectral differences.
- The theory aligns well with experimental observations.

## Abstract

The photoluminescence (PL) spectrum of transition metal dichalcogenides (TMDs) shows a multitude of emission peaks below the bright exciton line and not all of them have been explained yet. Here, we study the emission traces of phonon-assisted recombinations of momentum-dark excitons. To this end, we develop a microscopic theory describing simultaneous exciton, phonon and photon interaction and including consistent many-particle dephasing. We explain the drastically different PL below the bright exciton in tungsten- and molybdenum-based materials as result of different configurations of bright and dark states. In good agreement with experiments, we show that WSe$_2$ exhibits clearly visible low-temperature PL signals stemming from the phonon-assisted recombination of momentum-dark excitons.