Correlating ZnSe Quantum Dot Absorption with Particle Size and Concentration

23 August 2021, Version 4
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

The focus on heavy metal-free semiconductor nanocrystals has increased interest in ZnSe semiconductor quantum dots (QDs) over the past decade. Reliable and consistent incorporation of ZnSe cores into core/shell heterostructures or devices requires empirical fit equations correlating the lowest energy electron transition (1S peak) to their size and molar extinction coefficients (ε). While these equations are known and heavily used for CdSe, CdTe, CdS, PbS, etc., they are not well established for ZnSe and are non-existent for ZnSe QDs with diameters < 3.5 nm. In this study, a series of ZnSe QDs with diameters ranging from 2 to 6 nm were characterized with small angle X-ray scattering (SAXS), transmission electron microscopy (TEM), UV-Vis spectroscopy, and microwave plasma atomic emission spectroscopy (MP-AES). SAXS-based size analysis enabled practical inclusion of small particles in the evaluation, and elemental analysis with MP-AES elucidates a non-stoichiometric Zn:Se ratio consistent with zinc-terminated spherical ZnSe QDs. Using these combined results, empirical fit equations correlating QD size with its lowest energy electron transition (i.e., 1S peak position), Zn:Se ratio, and molar extinction coefficients for 1S peak, 1S integral, and high energy wavelengths are reported. Finally, the equations are used to track the evolution of a ZnSe core reaction. These results will enable the consistent and reliable use of ZnSe core particles in complex heterostructures and devices.

Keywords

quantum dot nanoparticles
zinc selenide
molar extinction coefficient
particle size
absorbance cross-section
intrinsic absorbance
high energy absorbance

Supplementary materials

Title
Description
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Title
ZnSe paper SI
Description
Supplementary figures including TEM images and sizing histograms, SAXS analysis, MP-AES calibration curves, application of intrinsic absorption coefficients, confirmation of molar extinction coefficient self-consistency, and reaction tracking comparing equations.
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