Nonexponential photoluminescence dynamics in an inhomogeneous ensemble of excitons in WSe$_2$ monolayers

TL;DR

This study investigates the complex, nonexponential photoluminescence decay in WSe₂ monolayers, revealing temperature and energy dependence, and proposes a model based on localized exciton states to explain the dynamics.

Contribution

It introduces a model accounting for spread in radiative recombination times of localized excitons, explaining nonexponential decay in WSe₂ monolayers.

Findings

Photoluminescence decay follows a 1/(t+t₀) dependence for times over 50 ps.

Decay accelerates with decreasing temperature and emission energy.

The dynamics are not due to bimolecular exciton-exciton annihilation.

Abstract

The spectral and spatiotemporal dynamics of photoluminescence in monolayers of transition metal dichalcogenide WSe$_2$ obtained by mechanical exfoliation on a Si/SiO$_2$ substrate is studied over a wide range of temperatures and excitation powers. It is shown that the dynamics is nonexponential and, for times $t$ exceeding $\sim$50 ps after the excitation pulse, is described by a dependence of the form $1/(t+t_0)$. Photoluminescence decay is accelerated with a decrease in temperature, as well as with a decrease in the energy of emitting states. It is shown that the observed dynamics cannot be described by a bimolecular recombination process, such as exciton--exciton annihilation. A model that describes the nonexponential photoluminescence dynamics by taking into account the spread of radiative recombination times of localized exciton states in a random potential gives good agreement with experimental data.