# Control of the Exciton Radiative Lifetime in van der Waals Heterostructures

## TL;DR

This paper demonstrates that the exciton radiative lifetime in van der Waals heterostructures can be precisely controlled by adjusting the hBN encapsulation layer thickness, leveraging the Purcell effect to tune emission times over an order of magnitude.

## Contribution

It introduces a method to control exciton radiative rates in 2D heterostructures through simple layer thickness modifications, supported by experimental and theoretical analysis.

## Key findings

- Radiative lifetime can be tuned by hBN thickness.
- Spontaneous emission time varies up to 10 ps.
- Enhanced or inhibited emission observed depending on configuration.

## Abstract

Optical properties of atomically thin transition metal dichalcogenides are controlled by robust excitons characterized by a very large oscillator strength. Encapsulation of monolayers such as MoSe$_2$ in hexagonal boron nitride (hBN) yields narrow optical transitions approaching the homogenous exciton linewidth. We demonstrate that the exciton radiative rate in these van der Waals heterostructures can be tailored by a simple change of the hBN encapsulation layer thickness as a consequence of the Purcell effect. The time-resolved photoluminescence measurements together with cw reflectivity and photoluminescence experiments show that the neutral exciton spontaneous emission time can be tuned by one order of magnitude depending on the thickness of the surrounding hBN layers. The inhibition of the radiative recombination can yield spontaneous emission time up to $10$~ps. These results are in very good agreement with the calculated recombination rate in the weak exciton-photon coupling regime. The analysis shows that we are also able to observe a sizeable enhancement of the exciton radiative decay rate. Understanding the role of these electrodynamical effects allow us to elucidate the complex dynamics of relaxation and recombination for both neutral and charged excitons.