Observation of Photoluminescence from a Natural van der Waals Heterostructure

TL;DR

This study reports the first observation of photoluminescence from the natural van der Waals heterostructure Franckeite, revealing excitonic emission properties and temperature dependence, with implications for nanoscale optoelectronic applications.

Contribution

It provides the first experimental evidence of photoluminescence from Franckeite, a natural heterostructure, and analyzes its optical properties and excitonic origins.

Findings

Photoluminescence peaks at ~1.93 eV and ~2.11 eV observed.

PL intensity decreases with increasing temperature.

PL quantum efficiency is lower than monolayer MoS₂.

Abstract

Van der Waals heterostructures comprised of two-dimensional (2D) materials offer a platform to obtain materials by design with unique electronic properties. Franckeite (Fr) is a naturally occurring van der Waals heterostructure comprised of two distinct alternately stacked semiconducting layers; (i) SnS$_2$ layer and (ii) Pb$_3$SbS$_4$. Though both layers in the heterostructure are semiconductors, the photoluminescence from Franckeite remains elusive. Here, we report the observation of photoluminescence (PL) from Franckeite for the first time. We observed two PL peaks at ~ 1.93 eV and ~ 2.11 eV. By varying the temperature from 1.5 K to 80 K, we found that the PL peak position redshifts and the integrated intensity decreases slowly as we increase the temperature. We observed linear dependence of photoluminescence integrated intensity on excitation laser power indicating that the photoluminescence is originating from free excitons in the SnS$_2$ layer of Fr. By comparing the PL from Fr with the PL from a monolayer MoS$_2$, we determined that the PL quantum efficiency from Fr is an order of magnitude lower than that of a monolayer MoS$_2$. Our study provides a fundamental understanding of the optical behavior in a complex naturally occurring van der Waals heterostructure, and may pave an avenue toward developing nanoscale optical and optoelectronic devices with tailored properties.