Page 20 - Read Online

Page 8 of 14 Jo et al. Soft Sci 2024;4:27 https://dx.doi.org/10.20517/ss.2024.19

Figure 3. (A-C) TEM images and size distribution histograms (insets); (D) absorption spectra normalized at the 1S peak; (E) normalized
PL spectra; and (F) variations of FWHM and PL QY of a series of InP-ZnX -Zn(OA) /ZnSe QDs. TEM: Transmission electron
2
2
microscopy; PL: photoluminescence; FWHM: full-width-at-half-maximum; QY: quantum yield; InP: indium phosphide; QDs: quantum
dots.
as a perfect reagent (vs. HCl and HBr), leaving unetched InPO residue. This scenario may be supported by
x
a marginal XPS signal trace of InPO from InP-ZnI -Zn(OA) unlike other two samples [Figure 2C]. In this
2
x
2
context, ZnBr is regarded as an optimal halide as it allows for not only the relevant ZnSe growth rate but
2
the near-complete removal of surface oxide, synergically rendering the heteroepitaxial shell growth perfect.
Meanwhile, InP-ZnX -Zn(OA) /ZnSe QDs with ZnCl and ZnBr exhibited nearly the same PL FWHM of
2
2
2
2
32 nm, while a markedly broad value of 37 nm resulted from InP-ZnI -Zn(OA) /ZnSe ones [Figure 3F].
2
2
Given the identical InP core, the major determinants of PL linewidth of InP/ZnSe QDs are the average
thickness and thickness uniformity of ZnSe shell. As noticed from size distributions [Figure 3A-C], InP-
ZnCl -Zn(OA) /ZnSe QDs possessed a relatively wide size distribution, i.e., lack of shell thickness
2
2
uniformity over individual QDs (resulting from an uncontrollably fast shell growth rate), when compared to
other two samples. Nevertheless, a sharp linewidth of InP-ZnCl -Zn(OA) /ZnSe QDs benefits from a
2
2
sufficiently thick ZnSe, which, in turn, can mitigate the exciton-phonon coupling strength via the increasing
delocalization of charge carriers . A broad linewidth of InP-ZnI -Zn(OA) /ZnSe QDs is likely ascribable to
[55]
2
2
the combined consequence of comparatively thin shell thickness and imperfect heteroepitaxial shell growth
(aforementioned), both of which have unfavorable effects on the reduction of exciton-phonon coupling
strength. Subsequent growth of the ZnS outer shell, for which the equimolar Zn(OA) and S-TOP were
2
identically used, on a series of InP-ZnX -Zn(OA) /ZnSe heterostructures above further boosted PL QY to
2
2
89%-100%, depending on the type of ZnX , while emission linewidths stayed the same [Figure 4]. Also refer
2
to Supplementary Figure 5 for the reproducible results of unity PL QYs from the representative three InP-
ZnBr -Zn(OA) /ZnSe/ZnS QD samples. Such superb emissive figures-of-merit possessing a narrow FWHM
2
2