Atomistic Origin of Photoluminescence Quenching in Colloidal MoS2 and WS2 Nanoplatelets

TL;DR

This paper investigates why certain nanostructures lose their light-emitting properties and finds that edge structures play a key role in this process.

Contribution

The study identifies edge-located hole traps as the origin of ultrafast exciton decay in TMD nanoplatelets.

Findings

Edge-located optically bright hole traps from metal d-orbitals cause sub-picosecond exciton decay.

WS2 has more localized and optically active edge states compared to MoS2.

Nanoplatelet size influences the competition between edge-trapping and core–exciton recombination.

Abstract

Large chemical tunability and strong light–matter
interactions
make colloidal transition metal dichalcogenide (TMD) nanostructures
particularly suitable for light-emitting applications. However, ultrafast
exciton decay and quenched photoluminescence (PL) limit their potential.
Combining femtosecond transient absorption spectroscopy with first-principles
calculations on MoS2 and WS2 nanoplatelets,
we reveal that the observed sub-picosecond exciton decay originates
from edge-located optically bright hole traps. These intrinsic trap
states stem from the metal d-orbitals and persist
even when the sulfur-terminated edges are hydrogen-passivated. Notably,
WS2 nanostructures show more localized and optically active
edge states than their MoS2 counterparts, and zigzag edges
exhibit a higher trap density than armchair edges. The nanoplatelet
size dictates the competition between ultrafast edge-trapping and
slower core–exciton recombination, and the states responsible
for exciton quenching enhance the catalytic activity. Our work represents
an important step forward in understanding exciton quenching in TMD
nanoplatelets and stimulates additional research to refine physicochemical
protocols for enhanced PL.

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