CdSexS1-x/ZnS quantum dots (QDs) can cover a broader spectral range than the commonly used CdSe/ZnS QDs and are potentially useful as biomarkers for tagging cell lines such as HeLa, A549, and MCF-7 due to their high photoluminescence intensity and stability in solution. So far, there have been few studies of colloidal CdSexS1-x/ZnS QDs that would simultaneously investigate changes in a) the molar composition of QD cores, and b) the shell thickness, as well as the effects of these changes on the photoluminescence and quantum yield properties of the QDs. CdSeyS1-y QDs and CdSexS1-x/ZnS core/shell QDs were synthesized via a previously reported and modified hot-injection procedure and via a telescoping one-pot synthesis based on the modified hot-injection procedure. Size, morphology, composition, and colloidal stability of these QD core/shell systems is reported with data obtained from TEM, XRD, TGA, DSC, DLS, and zeta potential techniques. Optical characterization is described using data collected from UV-Vis absorption spectrophotometry and photoluminescence spectroscopy.
Colloidal quantum dots (QDs) emitting in the near-infrared (NIR) spectrum are of interest for many biomedical applications, including bioimaging, biosensing, drug delivery, and photodynamic therapy. However, a significant limitation is that QDs are typically highly cytotoxic, containing materials such as indium arsenide (InAs), cadmium, or lead, which makes prospects for their FDA approval for human treatment very unlikely. Previous work on QDs in the NIR has focused on indium arsenide or cadmium chalcogenide cores coated with cadmium sulfide shells or zinc sulfide shells. Lead-based nanoparticles, such as lead selenide (PbSe) or lead sulfide (PbS) are also popular materials used for NIR emission. However, these nanoparticles have also been shown to be cytotoxic. Coating these Pb-based QDs with a biocompatible shell consisting of tin chalcogenides, such as tin sulfide (SnS) or tin selenide (TnSe), could be a reasonable alternative to improve their biocompatibility and reducing their cytotoxicity. In this paper, we report on our recent studies of PbSe-core QDs with Sn-containing shells, including synthesis, structural characterization, and investigation of optical properties. Characteristics of these QDs synthesized under different conditions are described. We conclude that their synthesis is challenging and still requires further work to avoid shell oxidation.
Anti-Stokes photoluminescence from colloidal CdSeS/ZnS quantum dots (QDs) is observed. The QDs were inserted into the core of wider-bandgap SiO2/Si3N4/SiO2 structure by thin film deposition and confirmed as promising nanoemitters for laser cooling due to efficient anti-Stokes emission. The nanoemitters were optically pumped by semiconductor lasers coupled to the waveguides using free-space optics. A direct evidence of local optical cooling in the waveguide structure has been demonstrated with a luminescence thermometry based on the detection of photoluminescence signal phase change versus power of the pumping laser, using a lock-in amplifier.