Abstract
Luminescent hexagonal dominant copper indium sulphide (h-dominant CIS) quantum dots (QDs) by precursor-injection of mixed metal-dialkyldithiocarbamate precursors. Owing to the different reactivity of the precursors, this method allowed the CIS QDs to grow while retaining the crystallinity of the hexagonal nucleus. The photoluminescence (PL) spectra exhibited dual emission (600–700 nm red emission and 700–800 nm NIR emission) resulting from the combined contributions of the hexagonal (wurtzite) h-CIS and tetragonal (chalcopyrite) t-CIS QDs, i.e. the NIR and red emissions were due to the h-CIS QDs and coexisting t-CIS QDs (weight ratio of h-CIS/t-CIS ~ 10), respectively. The PL intensities of the h-CIS as well as t-CIS QDs were enhanced by post-synthetic heat treatment; the t-CIS QDs were particularly sensitive to the heat treatment. By separating h-CIS and t-CIS successfully, it was demonstrated that this phenomenon was not affected by size and composition but by the donor-acceptor pair states and defect concentration originating from their crystal structure. The h-dominant CIS QDs in this work provide a new technique to control the optical property of Cu-In-S ternary NCs.
Highlights
Several factors affect the luminescence property of nanocrystals, such as the bandgap, size, composition, shape, and surface states[18]
We employed the precursor-injection method for the synthesis, in which the size of the quantum dots (QDs) was determined in the early nucleation stage
The crystal structures were characterised by X-ray diffraction (XRD) (Fig. 1a) and the [Cu]/[In] ratio obtained by inductively coupled plasma atomic emission spectroscopy (ICP-AES; Table 1)
Summary
Several factors affect the luminescence property of nanocrystals, such as the bandgap, size, composition, shape, and surface states[18]. [Cu]/[In] ratios and molecular formulas of h-dominant CIS QDs after growth, based on ICP-AES results. The overall PL intensities of CIS QDs increased upon post-synthetic heat treatment at 180 °C (Fig. 2).
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