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Recently, it was demonstrated that charge separation in hybrid metal–semiconductor nanoparticles (HNPs) can be obtained following photoexcitation of either the semiconductor or of the localized surface plasmon resonance (LSPR) of the metal. This suggests the intriguing possibility of photocatalytic systems benefiting from both plasmon and exciton excitation, the main challenge being to outcompete other ultrafast relaxation processes. Here we study CdSe-Au HNPs using ultrafast spectroscopy with high temporal resolution. We describe the complete pathways of electron transfer for both semiconductor and LSPR excitation. In the former, we distinguish hot and band gap electron transfer processes in the first few hundred fs. Excitation of the LSPR reveals an ultrafast (

Coupled colloidal quantum dot (CQD) dimers represent a new class of artificial molecules composed of fused core/shell semiconductor nanocrystals. The electronic coupling and wavefunction hybridization is enabled by the formation of an epitaxial connection with a coherent lattice between the shells of the two neighboring quantum dots where the shell material and its dimensions dictate the quantum barrier characteristics for the charge carriers. Herein we introduce a colloidal approach to control the neck formation at the interface between the two CQDs in such artificial molecular constructs. This allows the tailoring of the neck barrier in pre-linked homodimers formed via fusion of multifaceted wurtzite CdSe/CdS CQDs. The effects of reaction time, temperature and excess ligands is studied. The neck filling process follows an intraparticle ripening mechanism at relatively mild reaction conditions while avoiding inter-particle ripening. The degree of surface ligand passivation plays a key role in activating the surface atom diffusion to the neck region. The degree of neck filling strongly depends also on the initial relative orientation of the two CQDs, where homonymous plane attachment allows for facile neck growth, unlike the case of heteronymous plane attachment. Upon neck-filling, the observed red-shift of the absorption and fluorescence measured both for ensemble and single dimers, is assigned to enhanced hybridization of the confined wavefunction in CQD dimer molecules, as supported by quantum calculations. The fine tuning of the particle interface introduced herein provides therefore a powerful tool to further control the extent of hybridization and coupling in CQD molecules., Article- 19 pages, 5 figures; SI- 18 pages, 12 figures. Journal of the American Chemical Society Article ASAP, 2021

For visible range emitting particles, which are relevant for display and additional applications, Cd-chalcogenide nanocrystals have reached the highest degree of control and performance. Considering potential toxicity and regulatory limitations, there is a challenge to successfully develop Cd-free emitting nanocrystals and, in particular, heterostructures with desirable properties. Herein, we report a colloidal synthesis of fluorescent heavy-metal-free Zn-chalcogenide semiconductor nanodumbbells (NDBs), in which ZnSe tips were selectively grown on the apexes of ZnTe rods, as evidenced by a variety of methods. The fluorescence of the NDBs can be tuned between ∼500 and 585 nm by changing the ZnSe tip size. The emission quantum yield can be greatly increased through chloride surface treatment and reaches more than 30%. Simulations within an effective-mass-based model show that the hole wave function is spread over the ZnTe nanorods, while the electron wave function is localized on the ZnSe tips. Quantitative agreement for the red-shifted emission wavelength is obtained between the simulations and the experiments. Additionally, the changes in radiative lifetimes correlate well with the calculated decrease in electron-hole overlap upon growth of larger ZnSe tips. The heavy-metal-free ZnTe/ZnSe NDBs may be relevant for optoelectronic applications such as displays or light-emitting diodes.

Seeded semiconductor nanorods represent a unique family of quantum confined materials that manifest characteristics of mixed dimensionality. They show polarized emission with high quantum yield and fluorescence switching under an electric field, features that are desirable for use in display technologies and other optical applications. So far, their robust synthesis has been limited mainly to CdSe/CdS heterostructures, thereby constraining the spectral tunability to the red region of the visible spectrum. Herein we present a novel synthesis of CdSe/Cd1–xZnxS seeded nanorods with a radially graded composition that show bright and highly polarized green emission with minimal intermittency, as confirmed by ensemble and single nanorods optical measurements. Atomistic pseudopotential simulations elucidate the importance of the Zn atoms within the nanorod structure, in particular the effect of the graded composition. Thus, the controlled addition of Zn influences and improves the nanorods’ optoelectronic perfor...

Colloidal semiconductor nanocrystals (SCNCs) or, more broadly, colloidal quantum nanostructures constitute outstanding model systems for investigating size and dimensionality effects. Their nanoscale dimensions lead to quantum confinement effects that enable tuning of their optical and electronic properties. Thus, emission color control with narrow photoluminescence spectra, wide absorbance spectra, and outstanding photostability, combined with their chemical processability through control of their surface chemistry leads to the emergence of SCNCs as outstanding materials for present and next-generation displays. In this Review, we present the fundamental chemical and physical properties of SCNCs, followed by a description of the advantages of different colloidal quantum nanostructures for display applications. The open challenges with respect to their optical activity are addressed. Both photoluminescent and electroluminescent display scenarios utilizing SCNCs are described., Comment: 59 pages, 13 figures

Semiconductor heterostructure nanocrystals, especially with core/shell architectures, are important for numerous applications. Here we show that by decreasing the shell growth rate the morphology of ZnS shells on ZnSe quantum rods can be tuned from flat to islands-like, which decreases the interfacial strain energy. Further reduced growth speed, approaching the thermodynamic limit, leads to coherent shell growth forming unique helical-shell morphology. This reveals a template-free mechanism for induced chirality at the nanoscale. The helical morphology minimizes the sum of the strain and surface energy and maintains band gap emission due to its coherent core/shell interface without traps, unlike the other morphologies. Reaching the thermodynamic controlled growth regime for colloidal semiconductor core/shell nanocrystals thus offers morphologies with clear impact on their applicative potential., Core/shell semiconductor nanocrystals have advantageous optoelectronic properties, which depend on the shell architecture. Here the authors show that by reducing the growth rate of ZnS shells on ZnSe nanorods the shell morphology can be tuned from flat to islands-like to helical

Top-down fabricated nanoantenna architectures of both metallic and dielectric materials demonstrated powerful functionalities for Raman and fluorescence enhancement with relevance to single molecule sensing, while inducing directionality of chromophore emission with implications for single photon sources. Herein, we synthesize the smallest bowtie nanoantenna by selective tip-to-tip fusion of two tetrahedral colloidal quantum dots (CQDs) forming a dimer. While the tetrahedral monomers emit non-polarized light, the bowtie architecture manifests nanoantenna functionality of enhanced emission polarization along the bowtie axis as predicted theoretically and revealed by single particle spectroscopy. Theory also predicts the formation of an electric-field hotspot at the bowtie epicenter. This is utilized for selective light induced photocatalytic metal growth at that location, unlike growth on the free tips in dark conditions thus demonstrating the bowtie dimer functionality as a photochemical reaction center. Our findings pave a path for additional bottom-up bowtie architectures applicable in optics, sensing and photocatalysis., Comment: 9 pages, 5 figures