Quantum Dots In Solvents Research Articles

Fluoride ligand exchange for quantum dot light-emitting diodes with improved efficiency and stability

The ligands of quantum dots (QDs) not only play an important role in dispersion of the QDs in solvents and the protection of the QDs but could also block carrier injection into the QDs. Therefore, ligand engineering is important for improving performances of QD light-emitting diode (QLED) displays. In particular, exchange of an organic ligand with inorganic ones such as halides is expected to enhance efficiency and stability of QLED devices. In this study, an organic ligand on CdSe/ZnS QDs was exchanged with F− ligand in a non-polar solvent, which is suitable for device fabrication. As a result, stability of the QDs was improved, while the processability of QLED devices was maintained. Both external quantum efficiency of electroluminescence and device lifetime were improved, mainly because the thinner ligand layer improved the carrier injection efficiency.

Diffusion of fluorescent molecules and quantum dot nanoparticles in viscous solvents investigated by fluorescence correlation spectroscopy

AbstractThe fluorescence correlation spectroscopy (FCS) is a powerful measurement technique allowing the study of dynamic properties of fluorescent molecules and nanoparticles in solution environment with high sensitivity down to single molecule/particle level. In this paper we investigate the diffusion of Rhodamine B molecules and fluorescent quantum dots in solvents with different viscosities using a FCS instrument. The measured correlation functions show that the diffusion times of all molecules and quantum dots increase with the solvent viscosity. From the experimental data we derive the diffusion coefficients and hydrodynamic radii of the dye molecules and nanoparticles in different solvents using the Stokes – Einstein relation. Our results show that the diffusion times depend linearly on the solvent viscosity while the hydrodynamic radii remain approximately constant. The results will be useful for further study of the dynamics of molecules and nanoparticles in various biological environments.

Photoinduced Photoluminescence Variations of CdSe Quantum Dots in Polymer Solutions

Photoluminescence (PL) quantum efficiencies and lifetimes of CdSe quantum dots (QDs) were investigated under photoactivation in different chemical environments including polymer solutions and solvent systems. We observed considerable enhancement of the PL quantum efficiency of the QDs when photoactivated above the band gap in the presence of polymers such as poly(dimethyl siloxane) (PDMS), poly(vinyl pyrrolidone) (PVP), and poly(butadiene) (PBD). Furthermore, the PL spectra and the enhanced PL quantum efficiencies of the QDs were considerably stabilized under continuous photoactivation in the presence of dissolved polymers. Under photoactivation, the PL quantum efficiency was increased from 8% to 26−37% depending on the polymer environment. An increase of the PL quantum efficiency was also observed in solvents such as CHCl3 and n-butanol. However, photoactivation of the QDs in solvents with small dipole moments such as n-hexane and toluene resulted in substantial decreases of the PL quantum efficiency (fr...

Surface derivatization of nano-CdS clusters and its effect on the performance of CdS quantum dots in solvents and polymeric matrices

Synthesis of nanometer-sized clusters of CdS in inverse-micellar solution and in situ chemical derivatization of the surface of these cluster compounds were studied in the current paper. The nanoparticle surface can be terminated and passivated by the addition of imidazole and thiol molecules, which allows of inhibiting the particle from agglomeration, improving particle distribution in organic solvents and polymer matrices, and blocking surface defects that cause radiationless recombination of charge carriers. The solubility of these re-dispersible powders in different solvents was studied, and then the CdS quantum dots–polymer composites were prepared using solution mixing method. By means of optical, structural and thermal characterization techniques, the particle distribution and interfacial interaction in the composite systems and their influence on the properties of quantum CdS were revealed in detail.