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Jo et al. Soft Sci 2024;4:27 https://dx.doi.org/10.20517/ss.2024.19 Page 11 of 14

InP core and a series of InP/ZnSe QDs with varying ZnSe shell thicknesses. Figure 5F summarizes the strain
r e s u l t s o f I n P c o r e a n d I n P / Z n S e Q D s o b t a i n e d b y R a m a n s p e c t r o s c o p i c a n a l y s i s
[Supplementary Materials]. For InP/thin-ZnSe, ZnSe shell undergoes a high degree of tensile strain,
[57]
suggesting that it may form in the manner of somewhat partially island-shaped growth . Upon growth to
medium-ZnSe, the tensile strain becomes substantially relieved, indicating the formation of the coherent
ZnSe shell with complete coverage. In the case of InP/thick-ZnSe, the strain is further reduced, albeit
slightly, due to the continuing growth of ZnSe shell in the thermodynamically stable direction. Meanwhile,
the compressive strain of InP core consistently increases with a thicker growth of ZnSe shell. Judging from
the above strain analysis, the excessive compressive strain imposed on InP core by the growth of a thick-
ZnSe shell (exceeding a critical thickness) likely gives rise to the generation of interfacial defect and/or
misfit dislocation, thus entailing a decline of PL QY.

CONCLUSIONS
In green-emissive heterostructured InP QDs, the effects of the type of Zn precursor for shelling on shell
growth outcomes and consequent optical properties were investigated. When Zn halides were used for
shelling, the resulting InP/ZnSe/ZnS QDs overall possessed not only more uniform, spherical particle
morphologies but higher PL QYs compared to those shelled with the conventional Zn precursor of
Zn(OA) , benefiting from oxygen-free halide precursors that can suppress the formation of surface oxide
2
during shell growth. For an effort to remove the remnant surface oxide generated during core growth, a
hybrid Zn shelling process, where Zn halide and Zn(OA) were co-used as shell sources, was newly devised.
2
Our hypothesis that the surface oxide species can be effectively in-situ etched by a byproduct of hydrogen
halide released via the reaction of Zn(OA) with co-existing ZnX , was supported by the combined analytic
2
2
results of XPS and NMR. The growth rate and consequent thickness of ZnSe inner shell were sensitively
dependent on the type of ZnX in the hybrid Zn shelling process, showing the increasing thickness in the
2
order of ZnCl > ZnBr > ZnI (which was also rationalized with respect to the solute solubility and rate
2
2
2
constant of surface reaction). Among ZnX used, ZnBr was found to be an ideal halide as it enabled not
2
2
only the relevant ZnSe growth rate but the near-complete removal of the surface oxide. Upon ZnS outer
shelling on ZnBr -based InP/ZnSe QDs with an optimal ZnSe shell thickness, the resulting green QDs
2
produced a record PL QY of unity together with a sharp linewidth of 32 nm.
DECLARATIONS
Authors’ contributions
Made substantial contributions to the conception and design of the study: Yang H, Ryu CW, Jo DY
Performed data analysis and interpretation and wrote the manuscript: Jo DY, Kim HM, Ryu CW, Yang H
Provided administrative, technical, and material support: Park GM, Shin D, Kim Y, Kim YH

Availability of data and materials
Not applicable.

Financial support and sponsorship
This research was supported by the National Research Foundation of Korea (NRF) grant funded by the
Korean government (MSIT) (RS-2024-00411892, 2020M3H4A3082656) and the Technology Innovation
Program (20010737, 20016332) funded by the Ministry of Trade, Industry & Energy (MOTIE, Korea). This
work was also supported by the 2023 Hongik University Research Fund.

Conflicts of interest
All authors declared that there are no conflicts of interest.