Probing Excitons in Ultrathin PbS Nanoplatelets with Enhanced Near-Infrared Emission

TL;DR

This study investigates the excitonic properties of ultrathin PbS nanoplatelets using ultrafast spectroscopy, revealing enhanced near-infrared emission and improved photoluminescence quantum yield through surface treatment.

Contribution

It provides new insights into exciton dynamics in PbS NPLs and demonstrates a method to significantly boost their near-infrared emission efficiency.

Findings

Photoluminescence quantum yield increased from 1.4% to 19.4% after surface treatment.

Exciton-phonon interactions observed at 1.8 and 2.2 THz frequencies.

Ultrafast spectroscopy reveals exciton dynamics in ultrathin PbS NPLs.

Abstract

Strongly quantum-confined 2D colloidal PbS nanoplatelets (NPLs) are highly interesting materials for near-infrared optoelectronic applications. Here, we use ultrafast transient optical absorption spectroscopy to study the characteristics and dynamics of photoexcited excitons in ultrathin PbS NPLs with a cubic (rock-salt) structure. The NPLs are synthesized at near room temperature from lead oleate and thiourea precursors and show an optical absorption onset at 680 nm (1.8 eV) as well as photoluminescence at 720 nm (1.7 eV). By treating PbS NPLs with CdCl2 in a post-synthetic step, their photoluminescence quantum yield is strongly enhanced from 1.4 % to 19.4 %. The surface treatment leads to an increased lead to sulfur ratio in the structures and associated reduced non-radiative recombination. Exciton-phonon interactions in pristine and CdCl2 treated PbS NPLs at frequencies of 1.8 and 2.2 THz are apparent from coherent oscillations in the measured transient absorption spectra. This study is an important step forward in unraveling and controlling the optical properties of IV-VI semiconductor NPLs.