Correlating ZnSe Quantum Dot Absorption with Particle Size and Concentration

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 nonexistent 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 by 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 the practical inclusion of small particles in the evaluation, and elemental analysis with MP-AES elucidates a nonstoichiometric 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.

Chelation of Zn Cations as a Method for Their Replacement by Mn, Fe, Co in ZnSe Nanocrystals

“…The size of ZnSe NCs in question only allows metal excess up to 1.2‐fold theoretically and 1.1–1.15‐fold in practice. [ 25,26 ] This proves sulfide deposition at temperatures of 200 °C or higher. This temperature onset coincides well with Zn(DDTC) 2 thermal decomposition occurring at 195 °C.…”

No One Size Fits All: Semiconductor Nanocrystal Sizing Curves

“…Figure c shows that when TEM- and SAXS-based sizing curves are generated using the same ensembles with the same optical data ,,, SAXS indeed yields systematically larger NC sizes than TEM. This is highlighted by Tisdale’s PbS data (dash-dotted orange line), which can be disaggregated to yield TEM-exclusive and SAXS-exclusive sizing curves that agree well (see Table ).…”

“…Regarding sizing techniques, several studies have already shown that if TEM and SAXS measurements are conducted together, self-consistent agreement between techniques is possible. ,,,, Two key points should be considered though. First, SAXS and TEM perceive NC boundaries differently.…”

Phosphine-Free-Synthesized ZnSe/ZnS Core/Shell Quantum Dots for White Light-Emitting Diodes

“…This shift resulted from the increase in core size, and it indicated a size-dependent, electronic-energy band structure [33]. Consequently, a redshift in the absorption spectra of the ZnSe C QDs was observed with the growth of the ZnSe due to quantum confinement effects [33]. PL spectra also shifted from 413 nm to 425 nm with increasing reaction time.…”

“…The first absorption peak was observed at 407 nm for the aliquot taken at 5 min and continuously redshifted to 418 nm as the reaction time increased. This shift resulted from the increase in core size, and it indicated a size-dependent, electronic-energy band structure [33]. Consequently, a redshift in the absorption spectra of the ZnSe C QDs was observed with the growth of the ZnSe due to quantum confinement effects [33].…”