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Jo et al. Soft Sci 2024;4:27 https://dx.doi.org/10.20517/ss.2024.19 Page 5 of 14

Figure 1. (A) Variations of PL QY and peak wavelength; (B) absorption spectra; and (C-F) TEM images of green InP/ZnSe/ZnS QDs
synthesized with different Zn precursor types of ZnX (X = Cl, Br, I) and Zn(OA) for growth of ZnSe inner and ZnS outer shell. The
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double shell thicknesses of ZnSe/ZnS for individual QDs are also depicted in (C-F). The scale bars in (C-F) are all 20 nm. PL:
Photoluminescence; QY: quantum yield; TEM: transmission electron microscopy; InP: indium phosphide; QDs: quantum dots.
yielded the peak value of 89%. As compared in their absorption spectra normalized at the 1S peak
[Figure 1B], absorbance of InP-ZnX /ZnSe/ZnS QDs in blue-to-near UV region increased in the order of
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ZnI < ZnBr < ZnCl , while that of InP-Zn(OA) /ZnSe/ZnS QDs was slightly lower relative to InP-ZnBr /
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ZnSe/ZnS ones. Such a disparity in absorption is directly correlated with the thickness (or volume) of the
ZnSe shell [30,43] , indicative of the formation of the thickest and thinnest ZnSe shell for InP-ZnCl /ZnSe/ZnS
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and InP-ZnI /ZnSe/ZnS QDs, respectively. Being in line with the above absorption trend, the average sizes
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of a series of InP-ZnX /ZnSe/ZnS QDs systematically decreased from 10.2 [Figure 1C], 6.7 [Figure 1D] to
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5.3 nm [Figure 1E] for X = Cl, Br, I, respectively, while that of InP-Zn(OA) /ZnSe/ZnS ones was 6.0 nm
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[Figure 1F] (refer to Supplementary Figure 2 for the respective size distribution histograms). Note that InP-
ZnX /ZnSe/ZnS QDs overall possessed more uniform, spherical particle morphologies compared to InP-
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Zn(OA) /ZnSe/ZnS counterparts. Use of Zn carboxylate [e.g., Zn(OA) ] as a shell precursor is well-known
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to entail the generation of surface InPO during shell growth (as will be discussed later in more detail),
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which, in turn, renders the homogeneous growth of subsequent ZnSe shell difficult. In the case of InP/ZnSe
QD heterostructure, the thickness of ZnSe shell influences the band gap (consequently, PL) primarily owing
to the delocalization of electron wavefunction across the shell (which is more predominant in green-
emissive core due to a relatively small conduction band offset compared to red-emissive counterpart),
leading to the reduction in quantum confinement effects and consequently band gap from a thicker ZnSe
shell (refer to Supplementary Figure 3A magnified from Figure 1B). On that account, as presented in
normalized PL spectra of the above series of InP/ZnSe/ZnS QDs [Supplementary Figure 3B], PL peak
wavelength was well proportional to ZnSe shell thickness (e.g., the longest and shortest wavelengths of 538
and 530 nm from ZnCl - and ZnI -based InP/ZnSe/ZnS QDs, respectively). Aligning with the above results,
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