Linker-Assisted CdS-TiO2 Nanohybrids as Reusable Visible Light Photocatalysts for the Oxidative Hydroxylation of Arylboronic Acids

A variety of phenols have been obtained in aqueous media with moderate to excellent chemical yields (≤100%) by using arylboronic acids and esters as substrates, a robust CdS-TiO₂ nanohybrid as a heterogeneous photocatalyst, visible light irradiation (467 nm), and an O₂-saturated atmosphere. The nanohybrid was prepared through a linker-assisted methodology that uses mercapto alkanoic acids as the organic linkers. The nanohybrid showed improved photocatalytic activity in the hydroxylation of substituted arylboronic acids and phenyl boronic esters compared with that of pristine CdS quantum dots. The nanohybrid can be reused in up to five photocatalytic cycles with ∼90% of its outstanding activity preserved.

Origin of photoluminescence of water-soluble CuInS2 quantum dots prepared via a hydrothermal method

This study was performed to investigate the origin of the photoluminescence (PL) properties of hydrothermally-synthesized water-soluble CuInS₂ (CIS) quantum dots (QDs). The corresponding PL decay profiles, time-resolved PL spectra, and excitation intensity dependence of the PL spectra were evaluated. The decay profiles exhibited a strong dependence on the detection energy, and the peak of the time-resolved PL spectra shifted to lower energies with increasing time. With increasing excitation light intensity, the PL peak shifted to the high-energy side. These experimental results were consistent with the characteristics of donor–acceptor pair emission. The PL properties of Cu-doped and non-doped CdSe QDs, which show Cu-related and defect-related PL emission, respectively, were compared. Based on these results, it was concluded that donor–acceptor pair emission is the underlying mechanism of the PL of the hydrothermally-synthesized water-soluble CIS QDs.

The donor–acceptor pair emission is the underlying mechanism of the PL of the hydrothermally-synthesized water-soluble CIS QDs.

Controlling the dimension of the quantum resonance in CdTe quantum dot superlattices fabricated via layer-by-layer assembly

In quantum dot superlattices, wherein quantum dots are periodically arranged, electronic states between adjacent quantum dots are coupled by quantum resonance, which arises from the short-range electronic coupling of wave functions, and thus the formation of minibands is expected. Quantum dot superlattices have the potential to be key materials for new optoelectronic devices, such as highly efficient solar cells and photodetectors. Herein, we report the fabrication of CdTe quantum dot superlattices via the layer-by-layer assembly of positively charged polyelectrolytes and negatively charged CdTe quantum dots. We can thus control the dimension of the quantum resonance by independently changing the distances between quantum dots in the stacking (out-of-plane) and in-plane directions. Furthermore, we experimentally verify the miniband formation by measuring the excitation energy dependence of the photoluminescence spectra and detection energy dependence of the photoluminescence excitation spectra.

Designing quantum dot superlattices remains a challenge. Here, the authors present CdTe quantum dot superlattices via the layer-by-layer assembly and verify the miniband formation by measuring the excitation energy the dependence of the photoluminescence spectra and the detection energy dependence of the excitation spectra.

Coupled electronic states in CdTe quantum dot assemblies fabricated by utilizing chemical bonding between ligands

Semiconductor quantum dot superlattices (QDSLs) have attracted much attention as key materials for realizing new optoelectronic devices such as solar cells with high conversion efficiency and thermoelectric elements with high electrical conductivity. To improve the charge transport properties of QDSL-based optoelectronic devices, it is important that the QD structures form minibands, which are the coupled electronic states between QDs. A shorter inter-QD distance and a periodic arrangement of QDs are the essential conditions for the formation of minibands. In this study, we use CdTe QDs capped with short ligands of N-acetyl-l cysteine (NAC) to fabricate three-dimensional QD assemblies by utilizing chemical bonding between NACs. Absorption spectra clearly display the quantum resonance phenomenon originating from the coupling of the wave functions between the adjacent QDs in CdTe QD assemblies. Furthermore, we demonstrate the formation of minibands in CdTe QD assemblies by examining both, the excitation energy dependence of photoluminescence (PL) spectra and the detection energy dependence of PL excitation spectra. The fabrication method of QD assemblies utilizing chemical bonding between NACs can be applied to all QDs capped with NAC as a ligand.