Search for: All records

We investigated the pressure-dependent exciton absorption and photoluminescence (PL) properties of colloidal InAs/ZnSe core/shell quantum dots (QDs) emitting near-infrared (NIR) photons, an environmentally friendly alternative to heavy-metal-containing NIR QDs. A detailed analysis of exciton absorption and emission spectra was conducted in the pressure range of 0–10 GPa, focusing on the energy shifts, PL intensity, and lineshape changes with pressure. The pressure coefficients for exciton absorption and PL peaks were ∼70% of the bulk InAs value, with enhanced bandgap nonlinearity tentatively attributed to the higher bulk modulus of QDs compared to bulk material. The pressure-induced shifts in exciton absorption and PL peaks were reversible upon compression and decompression, with no indication of the semiconductor-to-metallic phase transition observed in bulk InAs around 7 GPa. However, PL intensity exhibited partial irreversibility, suggesting defect formation at the core/shell interface under pressure. From the findings of this study, along with previous high-pressure studies on molecular beam epitaxy-grown InAs QDs on GaAs, we infer the importance of the shell in determining the pressure response of exciton absorption and PL in core/shell QD structures with non-negligible interfacial strain and wave function spill into the shell. 

In this work, we investigated the effect of hole transporting poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) interfacing with Mn-doped CdS/ZnS quantum dots (QDs) deposited on an indium tin oxide (ITO) substrate on the photoemission of upconverted hot electrons under weak continuous wave photoexcitation in a vacuum. Among the various factors that can influence the photoemission of the upconverted hot electrons, we studied the role of PEDOT:PSS in facilitating the hole transfer from QDs and altering the energy of photoemitted hot electrons. Compared to hot electrons emitted from QDs deposited directly on the ITO substrate, the addition of the PEDOT:PSS layer between the QD and ITO layers increased the energy of the photoemitted hot electrons. The increased energy of the photoemitted hot electrons is attributed in part to the reduced steady-state positive charge on the QDs under continuous photoexcitation, which reduces the energy required to eject the electron from the conduction band. 

Lead-halide perovskite nanocrystals (NCs) are receiving much attention as a potential high-quality source of photons due to their superior luminescence properties in comparison to other semiconductor NCs. To date, research has focused mostly on NCs with little or no quantum confinement. Here, we measured the size- and temperature-dependent photoluminescence (PL) from strongly confined CsPbBr 3 quantum dots (QDs) with highly uniform size distributions, and examined the factors determining the evolution of the energy and linewidth of the PL with varying temperature and QD size. Compared to the extensively studied II–VI QDs, the spectral position of PL from CsPbBr 3 QDs shows an opposite dependence on temperature, with weaker dependence overall. On the other hand, the PL linewidth is much more sensitive to the temperature and size of the QDs compared to II–VI QDs, indicating much stronger coupling of excitons to the vibrational degrees of freedom both in the lattice and at the surface of the QDs. 

The efficient light-driven fuel production from homogeneous photocatalytic systems is one promising avenue towards an alternative energy economy. However, electron transfer from a conventional photosensitizer to a catalyst is short-range and necessitates spatial proximity between them. Here we show that energetic hot electrons generated by Mn-doped semiconductor quantum dots (QDs) allow for long-range sensitization of Ni(cyclam)-based molecular catalysts, enabling photocatalytic reduction of CO 2 to CO without requiring chemical linkages between the QDs and catalyst molecules. Our results demonstrate the potential of hot electron sensitization in simplifying the design of hybrid catalyst systems while improving photocatalytic activity.