Effect of sulfur solvent on the properties of lead sulfide quantum dots

Colloidal quantum dots (QDs) of lead sulfide have been synthesized and investigated using octadecene and white spirit as a solvent for sulfur, varying the concentration of precursors and the temperature of the process. A method has been proposed for the synthesis of these QDs using anhydrous white spirit as a solvent at a temperature of 200° C, which made it possible to obtain polygonal nanoparticles with an average diameter of 2 to 3.2 nm with a minimum spread in size (± 10%). Solvent white spirit, which has a low limiting solubility for sulfur and creates specific conditions for the reaction of the formation of lead sulfide at a high temperature (200° C), provides good synthesis kinetics in solution, a relatively low crystallization rate and creates conditions for the passage of all stages of the process from the formation of embryos before the maturation of the crystals. In this process, crystals of sufficiently stable sizes and shapes are steadily formed. It follows that the crystals are not spherical, but possibly somewhat rod-shaped, since their sizes differ in two directions. It is also seen that the sizes of QDs obtained using different concentrations of a sulfur solution in white spirit and varying the temperature differ insignificantly, since the confidence intervals are quite large and overlap. In one direction, the crystal size varies from 2 to 3.5 nm, and in the other from 3.5 to 5 nm. It has been found that at low temperatures the rate of reaction and crystal formation slows down. In this case, the anisotropic growth of crystals is pronounced, and the histogram curves are clearly divided into two regions. As a result, the transformation of the cubic structure of the crystal into a hexapod is noted. An increase in the concentration of lead in the reaction medium leads to a slight acceleration of the synthesis of nanoparticles.

Size Dependence of the Resonant Third-Order Nonlinear Refraction of Colloidal PbS Quantum Dots

Due to their high resonant third-order nonlinear response, lead sulfide quantum dots (QDs) are potential materials for applications in the field of nonlinear optics. In this paper, we implement the Z-scan method to study the resonant nonlinear response of lead sulfide QDs in colloidal solutions. We managed to measure the purely intrinsic resonant nonlinear response, free of thermal contribution. We report that the lead sulfide QD third-order nonlinear response per QD shows an unconventional increase. A figure of merit for QD nonlinearity grows as a power function with a factor of 2.9.

Charge Transfer from Lead Sulfide Quantum Dots to MoS-=SUB=-2-=/SUB=- Nanoplatelets-=SUP=-*-=/SUP=-

The research interest in the transition metal dichalcogenides (TMD) has been reborn a few years ago. This had happened due to the remarkable properties of monolayered TMD (e. g. high carrier mobility and high exciton binding energy) and due to the development of the exfoliation methods. Photoconductive MoS2-based devices spectral range can be expanded to the NIR by coupling them with PbS QDs. However, this requires extensive knowledge about the the charge and energy transfer processes in such systems. In this paper, we investigate charge transfer between PbS QDs and MoS2 nanoplatelets (NPls). Using the PL decay analysis, we show how the charge transfer efficiency changes with the distance between the QDs and NPls, as well as with QD size. Last, we demonstrate that the addition of the MoS2 NPLs increases the photoconductive response for up to an order of magnitude, as compared to the bare QD. Keywords: transition metal dichalcogenides, quantum dots, charge transfer, lead sulfide, molybdenum disulfide.