Disubstituted thiourea as a suitable sulfur source in the gram-scale synthesis of yellow- and red-emitting CdTeS/Cd x Zn1-x S core/shell quantum dots.

The key parameters of semiconductor quantum dots (QDs) that determine the suitability and efficiency for the design of most optoelectronic devices are the spectral positions of absorbance (ABS) and photoluminescence (PL) maxima, Stokes shift, photoluminescence quantum yield (PL QY) and photoluminescence lifetime (PL LT). All these parameters have been considered in the design of new ternary core CdTeS and core/shell CdTeS/Cd x Zn1-x S QDs. One-pot synthesis conducted in an organic medium at 160 °C using substituted thioureas as new, highly reactive sulfur sources allowed for the formation of a series of size- and emission-tunable CdTe0.05S0.95 QDs. Gram-scale synthesis of yellow-red emitting CdTe0.06S0.94 and CdTe0.12S0.88 cores was performed through the manipulation of their precursor ratio for the controllable formation of CdTeS/Cd x Zn1-x S (x = 0.1, 0.2, and 0.3) core/shell QDs. The development of the designed nanomaterials was carried out with a special emphasis on their optical properties, in particular a high PL QY up to 87% and extremely large Stokes shift, reaching ≈280 nm for core/shell QDs. Promisingly, for biolabeling and diagnostics, the synthesized core/shell QDs were transferred into water via surface ligand modification with the expected loss of photoluminescence efficiency. The results indicated that the availability of initial components, high yield of the desired product, stability in the organic phase, and high optical characteristics can scale up the synthesis of the developed nanomaterials from the laboratory level to industrial production.

Highly Efficient and Controllable Methodology of the Cd0.25Zn0.75Se/ZnS Core/Shell Quantum Dots Synthesis.

The surface of any binary or multi-component nanocrystal has imperfections and defects. The number of surface defects depends both on the nature of the nanomaterial and on the method of its preparation. One of the possibilities to confine the number of surface defects is the epitaxial growth of the shell, which leads to a change in the physical properties while maintaining the morphology of the core. To form a shell of the desired thickness, an accurate calculation of the amount of its precursors is substantial to avoid the appearance of individual crystals consisting of the shell material. This study aimed to develop an effective calculation method for the theoretical amount of precursors required for the formation of a ZnS shell on the surface of a Cd0.25Zn0.75Se core, followed by the practical implementation of theoretical calculations and characterization of the prepared nanomaterials. This method allows the complete control of the masses and volumes of the initial reagents, which will in turn prevent undesirable nucleation of nuclei consisting of the shell material. In the synthesis of Cd0.25Zn0.75Se/ZnS core/shell quantum dots (QDs), the sources of chalcogens were substituted seleno- and thioureas, which are capable of not only supplanting modern toxic sources of sulfur and selenium but also allowing one to perform the controlled synthesis of highly photoluminescent QDs with a low number of surface defects. The result of this shell overcoating method was an impetuous augmentation in the photoluminescence quantum yield (PL QY up to 83%), uniformity in size and shape, and a high yield of nanomaterials. The developed synthetic technique of core/shell QDs provides a controlled growth of the shell on the core surface, which makes it possible to transfer this method to an industrial scale.