Bright Fluorophores in the Second Near-Infrared Window: HgSe/CdSe Quantum Dots

TL;DR

This paper reports the synthesis of HgSe/CdSe core/shell quantum dots emitting at 1.7 microns with high quantum yields, advancing bioimaging potential in the NIR-IIb window by improving emission brightness.

Contribution

It introduces a novel synthesis method for HgSe/CdSe quantum dots with thick shells, significantly increasing their quantum yield for bioimaging applications.

Findings

Quantum yield of 55% in nonpolar solvents

Model explains quantum yields via FRET to ligands and solvents

Predicted >6% quantum yield in water

Abstract

Fluorophores emitting in the NIR-IIb wavelength range (1.5 micron - 1.7 micron) show great potential for bioimaging due to their large tissue penetration. However, current fluorophores suffer from poor emission with quantum yields ~2% in aqueous solvents. In this work, we report the synthesis of HgSe/CdSe core/shell quantum dots emitting at 1.7 microns through the interband transition. Growth of a thick shell led to a drastic increase in the photoluminescence quantum yield, with a value of 55% in nonpolar solvents. The quantum yields of our QDs and other reported QDs are explained well by a model of Forster resonance energy transfer to ligands and solvent molecules. The model predicts a quantum yield >6% when these HgSe/CdSe QDs are solubilized in water. Our work demonstrates the importance of a thick type-I shell to obtain bright emission in the NIR-IIb region