Effects of a Lead Chloride Shell on Lead Sulfide Quantum Dots

Abstract

The size of a quantum-confined nanocrystal determines the energies of its excitonic transitions. Previous work has correlated the diameters of PbS nanocrystals to their excitonic absorption; however, we observe that PbS quantum dots synthesized in saturated dispersions of PbCl2 can deviate from the previous 1Sh-1Se energy vs diameter curve by 0.8 nm. In addition, their surface differs chemically from that of PbS quantum dots produced via other syntheses. We find that these nanocrystals are coated in a shell that is measurable in transmission electron micrographs and contains lead and chlorine, beyond the monatomic chlorine termination previously proposed. This finding has implications for understanding the growth mechanism of this reaction, the line width of these quantum dots’ photoluminescence, and electronic transport within films of these nanocrystals. Such fundamental knowledge is critical to applications of PbS quantum dots such as single-photon sources, photodetectors, solar cells, light-emitting diodes, lasers, and biological labels.

Quantification of a PbClx Shell on the Surface of PbS Nanocrystals

“…These comparisons are consistent with SANS measurements on PbO-derived PbS QDs and suggest that neither the PbO route nor the PbCl 2 route with low excess PbCl 2 lead to a measurable PbCl x shell. 16 Ligand coverage agrees well with previous experimental measurements on PbS and PbSe in the range of 3−5 nm −2 . 27−29 Although the ligand coverage of the smallest QDs measured is high, it is does not exceed the maximum based on charge balance with excess lead atoms for a representative octahedral core shape.…”

Matrix Manipulation of Directly‐Synthesized PbS Quantum Dot Inks Enabled by Coordination Engineering

“…The surrounding PbI 2 matrix shell induces a tensile strain to expand the lattice constant, thereby shifting the Bragg peak to a smaller scattering angle. [ 38,43 ] In our case, the introduction of TBAI in the reaction can remove the excess PbI 2 in the QD film, which can release the tensile strain and shift the Bragg peak to a larger scattering angle, as seen in GIWAXS (Figure 2f). Consequently, GISAXS and GIWAXS results indicate that TBAI causes a better stacking behavior of the QDs in the final QD solid.…”

Nanocrystals of Lead Chalcohalides: A Series of Kinetically Trapped Metastable Nanostructures

“…81,82 Furthermore, recent work has demonstrated that PbS NCs synthesized from PbCl2 have a PbCl2 rich surface, leading to improved photoluminescence quantum yield and chemical stability, which might be related to the passivation by a layer of the hereby reported Pb3S2Cl2 phase. [83][84][85] This hypothesis may stimulate further studies aiming at a more detailed characterization of those systems.…”