Search

We explore the dynamics of energy transfer between two nanocrystal quantum dots placed within an optical microcavity. By adjusting the coupling strength between the cavity photon mode and the quantum dots, we have the capacity to fine-tune the effective coupling between the donor and acceptor. Introducing a non-adiabatic parameter, γ, governed by the coupling to the cavity mode, we demonstrate the system's capability to shift from the overdamped Förster regime (γ ≪ 1) to an underdamped coherent regime (γ ≫ 1). In the latter regime, characterized by swift energy transfer rates, the dynamics are influenced by decoherence time. To illustrate this, we study the exciton energy transfer dynamics between two closely positioned CdSe/CdS core/shell quantum dots with sizes and separations relevant to experimental conditions. Employing an atomistic approach, we calculate the excitonic level arrangement, exciton–phonon interactions, and transition dipole moments of the quantum dots within the microcavity. These parameters are then utilized to define a model Hamiltonian. Subsequently, we apply a generalized non-Markovian quantum Redfield equation to delineate the dynamics within the polaritonic framework. [ABSTRACT FROM AUTHOR]

In the search for materials alternate to bulk HgCdTe for high performance infrared imaging applications, colloidal quantum dots (CQDs), particularly HgTe CQDs, have gained traction owing to acceptable detector performance with easy preparation and low cost. In this article, we evaluate α -Sn CQDs, an environmentally less reactive and less toxic alternative to HgTe, for infrared sensing applications. Ab initio density functional theory calculations are used to study the shape-dependent stability, electronic bandgap, and absorption coefficient of α -Sn CQD nanoparticles (NPs). We consider three possible CQD shape constructions—Wulff, shell-by-shell, and spherical. The CQD of Wulff construction is predicted to be the most stable. However, we find that the size, not the shape, of the NP has a strong effect on the bandgap and absorption coefficient. Consequently, a sharp absorption edge is expected even in an ensemble of CQDs with different shapes. Importantly, the shape determines the position of the band edges with respect to vacuum, and thus offers a possibility of choosing the shape to improve alignment with the energy levels of ligands to enable efficient drift transport, instead of a slower and less efficient hopping transport. [ABSTRACT FROM AUTHOR]

Room temperature 6 μm intraband cascade electroluminescence (EL) is demonstrated with lightly n-doped HgTe colloidal quantum dots of ∼8 nm diameter deposited on interdigitated electrodes in a metal–insulator–metal device. With quantum dot films of ∼150 nm thickness made by solid-state-ligand-exchange, the devices emit at 1600 cm−1 (6.25 μm), with a spectral width of 200 cm−1, determined by the overlap of the 1Se–1Pe intraband transition of the quantum dots and the substrate photonic resonance. At the maximum current used of 20 mA, the bias was 30 V, the external quantum efficiency was 2.7%, and the power conversion efficiency was 0.025%. Adding gold nano-antennas between the electrodes broadened the emission and increased the quantum efficiency to 4.4% and the power efficiency to 0.036%. For these films, the doping was about 0.1 electron/dot, the electron mobility was 0.02 cm2 V−1 s−1, and the maximum current density was 0.04 kA cm−2. Higher mobility films made by solution ligand exchange show a 20-fold increase in current density and a 10-fold decrease in EL efficiencies. Electroluminescence with weak doping is interesting for eventually achieving electrically driven stimulated emission, and the requirements for population inversion and lasing are discussed. [ABSTRACT FROM AUTHOR]

Scintillators are materials that convert ionizing radiation in the form of particles or photons into low-energy photons in the ultraviolet to near-infrared spectral range. This work reviews efforts to use colloidal nanocrystals as scintillator materials. To date, research on colloidal nanocrystals as scintillators has focused on doped phosphor systems, quantum dots and related structures, and perovskite-based nanocrystals. Among various material classes and forms, colloidal semiconductor nanocrystals stand out thanks to their appealing fluorescence properties, yet understanding of their radioluminescence and cathodoluminescence is incomplete. This review discusses fundamental limits and material design challenges toward achieving high brightness, fast speed, and durable scintillator performance with nanocrystal scintillators. First, this review describes the basic principles and efficiency limitations of scintillation, particularly the large influence of multiple exciton generation in many nanocrystal species, as well as performance metrics. Second, methods for measurement are described. Third, we review the results of the main classes of nanocrystal scintillators, including quantum dots and related particles, perovskites, and doped-phosphor particles. Fourth, scintillation imaging is discussed in terms of the relevant performance metrics and results obtained using nanocrystal materials. Finally, we note the strengths and weaknesses of nanocrystal scintillators and discuss potential areas of further development. [ABSTRACT FROM AUTHOR]

The use of semiconductor nanocrystals in scalable quantum technologies requires characterization of the exciton coherence dynamics in an ensemble of electronically isolated crystals in which system–bath interactions are nevertheless strong. In this communication, we identify signatures of Fano-like interference between excitons and photocarriers in the coherent two-dimensional photoluminescence excitation spectral lineshapes of mixed lead-halide perovskite nanocrystals in dilute solution. Specifically, by tuning the femtosecond-pulse spectrum, we show such interference in an intermediate coupling regime, which is evident in the coherent lineshape when simultaneously exciting the exciton and the free-carrier band at higher energy. We conclude that this interference is an intrinsic effect that will be consequential in the quantum dynamics of the system and will thus dictate decoherence dynamics, with consequences in their application in quantum technologies. [ABSTRACT FROM AUTHOR]

In this paper, we study theoretically the electron and spectral properties of Ge 1 − x Sn x systems, including alloys, cubic- and spherical quantum dots. The single-particle electron and hole states are calculated within the s p 3 d 5 s ∗ tight-binding approach and used in further modeling of the optical properties. We systematically study the interplay of Sn-driven indirect–direct bandgap transition and the quantum confinement effect in systems of reduced dimensionality. We demonstrate the regime of sizes and compositions, where the ground state in Ge 1 − x Sn x quantum dots is optically active. Finally, we calculate absorbance spectra in experimentally relevant colloidal quantum dots and demonstrate satisfactory agreement with experimental data. [ABSTRACT FROM AUTHOR]

High fidelity single photon sources are required for the implementation of quantum information processing and communications protocols. Although colloidal quantum dots (CQDs) are single photon sources, their efficacy is limited by their tendency to show finite multiphoton emission at higher excitation powers. Here, we show that wave function engineering of CQDs enables the realization of emitters with significantly improved single photon emission performance. We study the ZnS/CdSe/CdS system. It is shown that this system offers significantly improved probabilities of single photon emission. While conventional CQDs such as CdSe/CdS exhibit a g2(0) > 0.5 ± 0.02 at ⟨N⟩ = 2.17, ZnS/CdSe/CdS show a greatly improved g2(0) ≈ 0.04 ± 0.01. Improved single photon emission performance encourages the use of colloidal materials as quantum light sources in emerging quantum devices. [ABSTRACT FROM AUTHOR]

Colloidal quantum dots are of increasing interest for mid-infrared detection and emission, but device performances will vastly benefit from reducing the non-radiative recombination. Empirically, the photoluminescence quantum yield decreases exponentially toward the mid-infrared, which appears similar to the energy gap law known for molecular fluorescence in the near-infrared. For molecules, the mechanism is electron–vibration coupling and fast internal vibrational relaxation. Here, we explore the possible mechanisms for inorganic quantum dots. The primary mechanism is assigned to an electric dipole near-field energy transfer from the quantum dot electronic transitions to the infrared absorption of surface organic ligands and then to the multiphonon absorption of the quantum dot inorganic core or the surrounding inorganic matrix. In order to obtain luminescent quantum dots in the 3–10 μm range, we motivate the importance of using inorganic matrices, which have a higher infrared transparency compared to organic materials. At longer wavelengths, inter-quantum dot energy transfer is noted to be much faster than radiative relaxation, indicating that bright mid-infrared colloidal quantum dot films might then benefit from dilution. [ABSTRACT FROM AUTHOR]

Semiconductor nanocrystals (NCs) can function as efficient gain materials with chemical versatility because of their surface ligands. Because the properties of NCs in solution are sensitive to ligand–environment interactions, local chemical changes can result in changes in the optical response. However, amplification of the optical response is technically challenging because of colloidal instability at NC concentrations needed for sufficient gain to overcome losses. This paper demonstrates liquid lasing from plasmonic lattice cavities integrated with ligand-engineered CdZnS/ZnS NCs dispersed in toluene and water. By taking advantage of calcium ion-induced aggregation of NCs in aqueous solutions, we show how lasing threshold can be used as a transduction signal for ion detection. Our work highlights how NC solutions and plasmonic lattices with open cavity architectures can serve as a biosensing platform for lab-on-chip devices. [ABSTRACT FROM AUTHOR]

A unique on-chip method for the direct correlation of optical properties, with atomic-scale chemical–structural characteristics for a single quantum dot (QD), is developed and utilized in various examples. This is based on performing single QD optical characterization on a modified glass substrate, followed by the extraction of the relevant region of interest by focused-ion-beam–scanning electron microscope processing into a lamella for high resolution scanning transmission electron microscopy (STEM) characterization with atomic scale resolution. The direct correlation of the optical response under an electric field with STEM analysis of the same particle allows addressing several single particle phenomena: first, the direct correlation of single QD photoluminescence (PL) polarization and its response to the external field with the QD crystal lattice alignment, so far inferred indirectly; second, the identification of unique yet rare few-QD assemblies, correlated directly with their special spectroscopic optical characteristics, serving as a guide for future designed assemblies; and third, the study on the effect of metal island growth on the PL behavior of hybrid semiconductor–metal nanoparticles, with relevance for their possible functionality in photocatalysis. This work, therefore, establishes the use of the direct on-chip optical–structural correlation method for numerous scenarios and timely questions in the field of QD research. [ABSTRACT FROM AUTHOR]

This article discusses a new fabrication process for colloidal silicon quantum dots (SiQDs) that allows for the tuning of their luminescence color from red to green. The process involves low-temperature thermal cracking of electrochemically prepared meso-porous silicon flakes in a mixture of 10-undecen-1-ol and aqueous hydrogen fluoride solution. The size of the SiQDs and their luminescence color can be controlled by adjusting the content of hydrogen fluoride. The article also explores the properties and potential applications of SiQDs in various fields, such as photovoltaic devices, light emitting devices, bio-imaging, and sensing. The document discusses the size-dependent radiative recombination processes of SiQDs, including factors that can affect their photoluminescence properties. It also explains the formation mechanisms of SiQDs and how they can result in different photoluminescence colors and peak wavelengths. The document concludes by discussing the relationship between the size of SiQDs and their photoluminescence peak energies, as well as the effect of surface passivation on quantum confinement. The article presents a novel method for producing SiQDs with tunable emission colors and suggests potential applications for SiQD devices. [Extracted from the article]

III–V colloidal quantum dots (QDs) promise Pb and Hg-free QD compositions with which to build short-wavelength infrared (SWIR) optoelectronic devices. However, their synthesis is limited by the availability of group-V precursors with controllable reactivities to prepare monodisperse, SWIR-absorbing III–V QDs. Here, we report a one-pot heat-up method to synthesize ∼8 nm edge length (∼6.5 nm in height) tetrahedral, SWIR-absorbing InAs QDs by increasing the [In3+]:[As3+] ratio introduced using commercially available InCl3 and AsCl3 precursors and by decreasing the concentration and optimizing the volume of the reducing reagent superhydride to control the concentration of In(0) and As(0) intermediates through QD nucleation and growth. InAs QDs are treated with NOBF4, and their deposited films are exchanged with Na2S to yield n-type InAs QD films. We realize the only colloidal InAs QD photoconductors with responsivity at the technologically important wavelength of 1.55 μm. [ABSTRACT FROM AUTHOR]

Transient absorption (TA) spectroscopy of semiconductor nanocrystals (NCs) is often used for excited state population analysis, but recent results suggest that TA bleach signals associated with multiexcitons in NCs do not scale linearly with exciton multiplicity. In this manuscript, we probe the factors that determine the intensities and spectral positions of exciton and biexciton components in the TA spectra of CdSe quantum dots (QDs) of five diameters. We find that, in all cases, the peak intensity of the biexciton TA spectrum is less than 1.5 times that of the single exciton TA spectrum, in stark contrast to a commonly made assumption that this ratio is 2. The relative intensities of the biexciton and exciton TA signals at each wavelength are determined by at least two factors: the TA spectral intensity and the spectral offset between the two signals. We do not observe correlations between either of these factors and the particle diameter, but we find that both are strongly impacted by replacing the native organic surface-capping ligands with a hole-trapping ligand. These results suggest that surface trapping plays an important role in determining the absolute intensities of TA features for CdSe QDs and not just their decay kinetics. Our work highlights the role of spectral offsets and the importance of surface trapping in governing absolute TA intensities. It also conclusively demonstrates that the biexciton TA spectra of CdSe QDs at the band gap energy are less than twice as intense as those of the exciton. [ABSTRACT FROM AUTHOR]

Complicated nano- and atomic-scale processes with sub-angstrom spatial resolution and millisecond time resolution visualized by in situ transmission electron microscopy (TEM) are often highly dynamical and time consuming to analyze and interpret. Here, we report how variational autoencoders (VAEs) can provide an artificial intelligence's interpretation of high-resolution in situ TEM data by condensing and deconvoluting complicated atomic-scale dynamics into a latent space with reduced dimensionality. We designed a VAE model with high latent dimensions capable of deconvoluting information from complex high-resolution TEM data. We demonstrate how this model, with high latent dimensions trained on atomically resolved TEM images of lead sulfide (PbS) nanocrystals, is able to capture movements and perturbations of periodic lattices in both simulated and real in situ TEM data. The VAE model shows the capability of detecting and deconvoluting dynamical nanoscale physical processes, such as the rotation of crystal lattices and intra-particle ripening during the annealing of semiconductor nanocrystals.

Colloidal quantum dots, with their size-tunable optoelectronic properties and scalable synthesis, enable applications in which inexpensive high-performance semiconductors are needed. Synthesis science breakthroughs have been key to the realization of quantum dot technologies, but important group III- group V semiconductors, including colloidal gallium arsenide (GaAs), still cannot be synthesized with existing approaches. The high-temperature molten salt colloidal synthesis introduced in this work enables the preparation of previously intractable colloidal materials. We directly nucleated and grew colloidal quantum dots in molten inorganic salts by harnessing molten salt redox chemistry and using surfactant additives for nanocrystal shape control. Synthesis temperatures above 425°C are critical for realizing photoluminescent GaAs quantum dots, which emphasizes the importance of high temperatures enabled by molten salt solvents. We generalize the methodology and demonstrate nearly a dozen III-V solid-solution nanocrystal compositions that have not been previously reported. [ABSTRACT FROM AUTHOR]

InSb colloid quantum dots (CQDs) are liquid “green” semiconductor materials. Their band gaps can be readily adjusted by controlling their particle size. Their excellent photoelectric properties and non‐toxic properties render them highly suitable for the fabrication of low‐cost infrared photodetectors and image sensors in industrial and consumer electronics applications. Despite the concept and preparation of InSb CQDs having been reported for decades, the performance of InSb CQDs‐based photodetectors still lags behind that of their toxic PbS CQDs‐based counterparts. This is mainly due to the immature synthesis process and the lack of sufficient device research. Fortunately, significant advances have been made in the synthesis of InSb CQDs and ligand exchange strategies over the past three years, resulting in notable enhancements in device performance. This review presents a summary of the recent advances in InSb CQDs and their applications in photodetectors. A particular focus is placed on the development of controllable synthesis routes for high‐quality InSb CQDs, which represents a significant challenge due to the high valence nature of InSb. Furthermore, the performance of these devices is discussed in detail, with a particular focus on ligand exchange and surface treatment strategies. Finally, a brief summary and outlook on InSb CQDs‐based photodetectors is presented. [ABSTRACT FROM AUTHOR]

Solution‐processable colloidal quantum dots (QDs) are regarded as promising light emitters for next‐generation displays owing to their high photoluminescence quantum yield (PLQY) and broad color tunability. Even though cadmium (Cd)‐based QDs and relevant electroluminescent light‐emitting diodes (LEDs) progressed rapidly, their commercial deployment remains prohibited due to potential environmental concerns. In this review, recent advances in synthesizing eco‐friendly, bright, and color‐pure emitting QDs including InP, ZnSeTe, and AgInGaS2 (AIGS) QDs toward high‐performing LEDs are presented. In particular, the synthetic strategies such as regulating the composition, core/shell structure, and surface ligands of QDs for enhancing the PLQY and reducing the spectral bandwidth are comprehensively discussed. Moreover, various techniques to obtain high‐performance QDs‐based LEDs (QLEDs) involving device architecture and interface engineering as well as modification in electron and hole transport layers are overviewed. Finally, the existing challenges and outlook regarding the optimization of QD's synthesis and optical properties for boosted QLEDs device performance are put forward to enable prospective advanced displays. [ABSTRACT FROM AUTHOR]

Perfluoroalkyl substances (PFASs) and fluorinated polymers (FPs) have been extensively utilized in various industries, whereas their extremely high stability poses environmental persistence and difficulty in waste treatment. Current decomposition approaches of PFASs and FPs typically require harsh conditions such as heating over 400 °C. Thus, there is a pressing need to develop a new technique capable of decomposing them under mild conditions. Here, we demonstrated that perfluorooctanesulfonate (PFOS), known as a "persistent chemical," and Nafion, a widely utilized sulfonated FP for ion‐exchange membranes, can be efficiently decomposed into fluorine ions under ambient conditions via the irradiation of visible LED light onto semiconductor nanocrystals (NCs). PFOS was completely defluorinated within 8‐h irradiation of 405‐nm LED light, and the turnover number of the C−F bond dissociation per NC was 17200. Furthermore, 81 % defluorination of Nafion was achieved for 24‐h light irradiation, demonstrating the efficient photocatalytic properties under visible light. We revealed that this decomposition is driven by cooperative mechanisms involving light‐induced ligand displacements and Auger‐induced electron injections via hydrated electrons and higher excited states. This study not only demonstrates the feasibility of efficiently breaking down various PFASs and FPs under mild conditions but also paves the way for advancing toward a sustainable fluorine‐recycling society. [ABSTRACT FROM AUTHOR]

In recent years, academic research on perovskite solar cells (PSCs) has attracted remarkable attention, and one of the most crucial issues is promoting the power conversion efficiency (PCE) and operational stability of PSCs. Generally, modification of the electron or hole transport layers between the perovskite layers and electrodes via surface engineering is considered an effective strategy because the inherent structural defects between charge carrier transport layers and perovskite layers can be reshaped and modified by adopting the functional nanomaterials, and thus the charge recombination rate can be naturally decreased. At present, large amounts of available nanomaterials for surface modification of the perovskite films are extensively investigated, mainly including nanocrystals, nanorods, nanoarrays, and even colloidal quantum dots (QDs). In particular, as unique size-dependent nanomaterials, the diverse quantum properties of colloidal QDs are different from other nanomaterials, such as their quantum confinement effects, quantum-tunable effects, and quantum surface effects, which display great potential in promoting the PCE and operational stability of PSCs as the charge carriers in perovskite layers can be effectively tuned by these quantum effects. However, preparing QDs with a neat and desirable size remains a technical difficulty, even though the present chemical engineering is highly advanced. Fortunately, the rapid advances in laser technology have provided new insight into the precise preparation of QDs. In this review, we introduce a new approach for preparing the QDs, namely pulsed laser irradiation in colloids (PLIC), and briefly highlight the innovative works on PLIC-prepared QDs for the optimization of PSCs. This review not only highlights the advantages of PLIC for QD preparation but also critically points out the challenges and prospects of QD-based PSCs. [ABSTRACT FROM AUTHOR]

Objective: Modern neurobiology focuses on understanding and preventing neurodegeneration by detecting cellular changes early. Changes in astrocyte ultramorphology may indicate early neurodegeneration, associated with decreased synaptic plasticity and astrocyte aging. While high-resolution techniques like EM and SPM can study these structures, they can't use fluorescence microscopy for complete 3D analysis. We suggest using fluorescent dye-conjugated nanoantibodies for astrocyte labeling, allowing detailed ultramorphological research with electron, optical, and scanning probe microscopy, plus optical probe nanotomography. Methods: Hippocampi from male C57BL/6 mice were stained using commercial or GFAP-specific VHH-E9 nanoantibodies. The VHH-E9 antibodies were created by synthesizing a nucleotide sequence with added histidines and cysteine, then cloning it into the pET22 plasmid at XbaI and BamHI sites. Escherichia coli Rosetta-gami (DE3) cells were transformed to produce the pET22-VHHE9 strain. The nanoantibodies were produced via autoinduction and conjugated with a fluorophore. Astrocyte morphology was analyzed using the Sholl test with FiJi software. Results and Discussion: Traditional immunoglobulins can cause visualization inaccuracies due to the distance between the label and target protein. Nanoantibody conjugates, being smaller, reduce these errors. Immunostainings with both types showed similar efficiency, as Sholl profiles from different samples aligned within error margins. This supports the effectiveness of the sample preparation method and VHH-E9 nanoantibodies. It also suggests potential for developing similar procedures with fluorescent contrast agents, like semiconductor nanocrystals. Conclusions: To study astrocyte changes in early neurodegenerative stages, we propose combining high-resolution microscopy, optical microspectroscopy, and 3D ultrastructure restoration. Our method, OPNT, uses fluorescence microscopy for localization data, and SPM/UMT for ultrastructure. This involves creating UMT sections for simultaneous OM/SPM analysis and reconstructing them into a 3D array. We efficiently reconstruct 3D astrocyte ultramorphology and developed an immunostaining procedure using camel VHH-E9 nanoantibodies specific to GFAP, highlighting its efficiency and potential with fluorescent semiconductor nanocrystals. [ABSTRACT FROM AUTHOR]

Colloidal InSb quantum dots (QDs) are a potential alternative to toxic Pb‐ and Hg‐chalcogenide QDs for covering the technologically important near‐infrared/shortwave infrared (NIR/SWIR) spectral range. However, appropriate Sb precursors are scarce and obtaining narrow size distributions is challenging. Tris(dimethylamido)antimony (Sb(NMe2)3) is an appealing choice due to its commercial availability and non‐pyrophoric character but implies the reduction of antimony from the +3 to the required –3 state. In reported works, strong reducing agents such as lithium triethylborohydride are used, which lead to the fast co‐reduction of both Sb3+ and In3+. The downsides of this approach are reproducibility issues and the risk of forming metal nanoparticles due to the different reduction kinetics of Sb3+ and In3+. Here, indium(I) halides are explored as simultaneous indium source and mild reducing agent for the antimony precursor. The wavelength of the excitonic absorption peak of the phase‐pure InSb QDs obtained with this approach can be tuned from 630 to 1890 nm, which corresponds to a size range of ≈2–7 nm. The synthesis can also be conducted in a heat‐up manner, which facilitates the scale‐up and paves the way for the use of InSb QDs in applications such as NIR/SWIR photodetectors, cameras, biological imaging, and telecommunications. [ABSTRACT FROM AUTHOR]

High‐resolution infrared (IR) imaging technology holds substantial significance across diverse fields including biomedical imaging, environmental surveillance, and IR digital cameras. Current IR detectors used in commercial applications are based on ultra‐high vacuum‐processed traditional inorganic semiconductors like silicon or III‐V compounds (e.g., Si, Ge, and InGaAs). However, the rapid advancements in applications such as autonomous vehicles, virtual reality, and point‐of‐care healthcare are driving an escalating need for innovative imaging technologies. This review aims to bridge the gap by exploring solution‐processed semiconductor photodetectors (PDs), which offer distinct advantages including cost‐effectiveness, tunable spectral response, and potential for multiple‐exciton generation. These characteristics make them particularly suitable for optical communication, IR imaging, and biological monitoring applications. This review provides comprehensive insights into the research trends pertaining to solution‐processed IR detectors and imagers based on colloidal quantum dots, perovskites, organic compounds, and 2D materials. The review commences with the current market worth of image sensors, the fundamental principles of single‐pixel and multipixel array IR imagers, and key parameters used to assess IR detector performance. In essence, the review concludes with a summary of recent advancements and future prospects for next‐generation IR PD devices and their potential application as an IR imager. [ABSTRACT FROM AUTHOR]

The development of optoelectronic devices based on III–V semiconductor colloidal quantum dots (CQDs) is highly sought after due to their reduced toxicity. While devices based on conventional CQDs (II–VI semiconductors, halide perovskites) have achieved impressive technological leaps since their discovery, the most mature of these compounds contain toxic heavy metal elements (Cd, Hg, or Pb), which are highly undesirable for safe industrial scale applications. The strong covalent bonds of III–V compounds like InP, InAs, or InSb prevent the release of their toxic atoms, making them safer. However, these same bonds create severe material constraints. Namely, their harsher reaction conditions and increased sensitivity to oxidation have kept most of the research focused on material development. Meanwhile, their integration into devices and their coupling to photonic structures lag behind. Here, the integration of InAs/ZnSe core‐shell CQDs is advanced. First, the material parameters necessary to design plasmonic gratings coupled to the CQDs are elucidated and those gratings are fabricated. Angle‐resolved spectroscopy shows that the plasmon modes successfully couple to the CQD layer's emission leading to a tunable directivity with a 15° linewidth. A 3‐fold increase of the PL signal is achieved at normal incidence, thus advancing toward the goal of efficient outcoupling in LEDs. [ABSTRACT FROM AUTHOR]

Colloidal quantum dots (CQDs) are promising semiconductors for optoelectronic applications owing to their bandgap tunability and solution processability. Historically, ethanedithiol has been widely employed as a surface ligand to form a p‐type CQD layer via a layer‐by‐layer process. However, the limited control of p‐type characteristics reduces the device performance, and the high reactivity of ligand and processing solvents degrade the underlying layer. In this study, a thiol‐free p‐type CQD is demonstrated by creating native p‐type CQDs during the synthesis process. Sulfurization of PbS CQD results in p‐type properties that enable the avoidance of any further thiol‐ligand treatment process. Further, alternative surface passivation of the sulfurized CQD using halide ligand yields a robust, p‐type, morphologically uniform, and trap‐suppressed film. The developed CQD film is then employed as a hole‐transporting layer (HTL) for both broadband solar cells and photodetectors. The resulting CQD devices exhibit improved performance with a 65.7% increase in photovoltaic efficiency and a 1.7‐fold improvement in responsivity for infrared photodetection. The devices also demonstrate higher ambient stability, retaining 85% of the initial performance after 1,000 hr owing to the uniform top HTL morphology, indicating the potential of the new p‐type layer to be utilized in various emerging optoelectronics. [ABSTRACT FROM AUTHOR]

Among materials produced as colloidal quantum dots (CQDs), HgTe has a special status being the only material covering the whole infrared range from the visible to the THz (0.7–100 µm). This unique property resulting from its electronic structure, combined with an air stability and a capacity for charge conduction has generated consistent and massive efforts to produce and improve HgTe CQDs over the past two decades. Meanwhile, HgTe CQDs offer an infrared platform more advanced than any other colloidal alternatives in the mid‐wave infrared regarding their integration into advanced photonic and optoelectronic applications. Here, the latest developments of HgTe CQDs relative to the material's growth, electron structure modelling, its integration into photonic structures and its transfer as the active material from single element devices toward complex sensors and infrared imagers are reviewed. Finally, a discussion about the potential of this material for industry, rising new challenges beyond economical and production considerations at low technological readiness level, relative to the material and device design, is also included. [ABSTRACT FROM AUTHOR]

In the last twenty years, nanofabrication progress has allowed for the emergence of a new photodetector family, generally called low-dimensional solids (LDSs), among which the most important are two-dimensional (2D) materials, perovskites, and nanowires/quantum dots. They operate in a wide wavelength range from ultraviolet to far-infrared. Current research indicates remarkable advances in increasing the performance of this new generation of photodetectors. The published performance at room temperature is even better than reported for typical photodetectors. Several articles demonstrate detectivity outperforming physical boundaries driven by background radiation and signal fluctuations. This study attempts to explain these peculiarities. In order to achieve this goal, we first clarify the fundamental differences in the photoelectric effects of the new generation of photodetectors compared to the standard designs dominating the commercial market. Photodetectors made of 2D transition metal dichalcogenides (TMDs), quantum dots, topological insulators, and perovskites are mainly considered. Their performance is compared with the fundamental limits estimated by the signal fluctuation limit (in the ultraviolet region) and the background radiation limit (in the infrared region). In the latter case, Law 19 dedicated to HgCdTe photodiodes is used as a standard reference benchmark. The causes for the performance overestimate of the different types of LDS detectors are also explained. Finally, an attempt is made to determine their place in the global market in the long term. [ABSTRACT FROM AUTHOR]

New asymmetrical pyridyl-BODIPY dyes with a meso-CF3-group were synthesized by condensation of trifluoro-1-(5-phenylpyrrol-2-yl)ethanol with 2-(2-, 3- or 4-pyridyl)pyrroles, followed by the oxidation and formation of a complex with BF3 etherate. The molecular and crystal structures of these compounds were studied by DFT calculations and single-crystal X-ray diffraction analysis. The absorption and fluorescence properties of the synthesized dyes in polar and nonpolar media were quantitatively characterized. In this work, the efficiency of dye adsorption on CdSe colloidal quantum dots was studied, and the influence of the nitrogen atom position in the pyridyl group on the stability of the resulting associates was shown. [ABSTRACT FROM AUTHOR]

Solution‐processed quantum dot‐based near and short‐wave infrared light emitters have witnessed substantial developments in recent years. A variety of colloidal quantum dots (CQDs)‐based light emitters, including light‐emitting diodes, optical down‐converters, and emitters showing amplified spontaneous emission, lasing in the near and short‐wave infrared region, are demonstrated over the years. The progress in chemical synthesis of CQDs, development of novel CQDs, better understanding of the surface properties, chemical treatments to improve the optoelectronic properties, and suitable device engineering led to tremendous advances in the light emission performance in the near and short‐wave infrared region. A broad investigation is done into various CQD materials to achieve efficient near‐infrared light emitters. This review gives a detailed account of the advancement of the CQD‐based near and short‐wave infrared light emitters, strategies to improve the optoelectronic performance, controlling optical properties, demonstrated applications, the challenges that need to be tackled for further development, and future research direction. [ABSTRACT FROM AUTHOR]

Due to their internal gain mechanism, emerging nanomaterial‐based infrared phototransistors show significant promise for highly sensitive detection; however, they usually suffer from high dark current (Idark) and thus high noise, which restricts the actual detection capability of the detector. Here, a semiconducting carbon nanotube (CNT) film‐based phototransistor is proposed with an ultralow Idark and a high response through the adoption of stacked ZnO/PbS colloidal quantum dot heterojunctions as the photogate to absorb the infrared photons and generate a photovoltage. Solution‐derived semiconducting CNTs with diameters ranging from 0.8 to 1.1 nm are utilized to create a network film that serves as the active channel of the transistor and provides an off‐state current as low as ≈50 fA; this enables an ultralow dark current (pA level) in the infrared phototransistor. By tuning the back‐gate bias, the synergistic modulation is demonstrated of the sensor response and electronic noise and achieve a high detectivity of 5.7 × 1013 Jones under an incident power density of 0.81 nW cm−2 and 1300 nm infrared radiation. These findings provide a promising approach for attaining weak light infrared detection based on nanomaterial‐based photodetectors. [ABSTRACT FROM AUTHOR]

The "Nobel Prize in Chemistry 2023" is awarded to Moungi G. Bawendi, Louis E. Brus, and Alexey I. Yekimov for discovering and synthesizing Quantum Dots (QDs). Colloidal QDs possess fascinating size‐, morphological‐, composition‐, and assembly‐tunable electronic and optical properties, which makes them star materials for various optoelectronic applications, especially as luminescent materials for next‐generation wide color gamut ultra‐high‐definition displays. Perovskite QDs (PQDs) have gained widespread attention in recent years. In less than ten years, research on perovskite‐related materials and devices has basically been perfected in terms of quantum yield and external quantum efficiency (EQE). However, on the eve of its industrial application, some key technical indicators and technical processes need to be met and resolved. The development and transformation of QD materials and then focuses on the progress of luminescence linewidth and EQE of the PQD light‐emitting diode. Finally, several application avenues are reviewed for PQDs, and some challenges and opportunities in the field are proposed. [ABSTRACT FROM AUTHOR]

Solar energy storage technology ensures a sustainable and reliable energy supply. Herein, we show that electrons generated in semiconductor nanocrystals (NCs) of CsPbBr3 by visible light excitation can be stored in polyoxometalates (POMs) of W10O32, and extracted as an electric current using a photoelectrochemical cell. [ABSTRACT FROM AUTHOR]

The optical properties of strongly doped semiconductor nanocrystals depend strongly on the carrier density of the nanocrystals. These characteristics can be exploited for the design of innovative optical devices based on ultrafast switching potentially in the THz modulation bandwidth. In this study, the optical response of one‐dimensional photonic crystals incorporating colloidal nanoparticles of a highly doped semiconductor such as indium tin oxide (ITO) is investigated, taking into consideration the angular dependence of the photonic band gap and the position dependence of the photonic band gap on the light‐induced tunability of the ITO doping. [ABSTRACT FROM AUTHOR]

Localized surface plasmon resonance (LSPR) in plasmonic nanomaterials can concentrate light in the nano‐dimension, leading to an enhancement of the light intensity by order of magnitude. While LSPR is a subject of extensive research in chalcogenide semiconductor nanocrystals (NCs), research on tellurium multinary chalcogenides (MnCs) remains elusive, possibly due to non‐availability of the corresponding quantum dots (QDs). In this report, we show the sequential switching of plasmonic to non‐plasmonic properties during the colloidal synthesis of AgInTe2 QDs. The reaction passes through several intermediates including AgInTe2/AgIn5Te8 core/shell NCs, AgInTe2 microrods (MRs), AgInTe2 QDs, and finally AgInTe2 quantum dot chain (QDC). Here, the AgInTe2/AgIn5Te8 core/shell NCs and AgInTe2 QDs depict strong LSPR absorption in the visible‐NIR region until ~2000 nm. We propose that small‐size quantum confined and cation deficient AgInTe2 particles are responsible for the observation of LSPR modes in both cases due to presence of the free carriers (holes). Our work on developing Te‐based plasmonic MnC QDs may find significant advancement in the nanoscale light‐matter interaction in semiconductor research. [ABSTRACT FROM AUTHOR]

Deep-red light has significant application value in various fields, including biomedicine, plant cultivation, and displays. The development of high-efficiency deep-red luminescent materials is therefore of great importance. Semiconductor nanocrystals have been extensively studied as novel luminescent materials due to their wavelength tunability, narrow emission linewidth, and high luminescence efficiency. However, the advancement of deep-red nanocrystals has lagged behind that of red, green, and blue nanocrystals, primarily due to material selection limitations. This review summarizes the recent progress in the synthesis of deep-red nanocrystals based on their material composition, including II-VI, III-V, I-III-VI, and perovskite nanocrystals. [ABSTRACT FROM AUTHOR]

Organic conjugated polymers have received extensive attention due to their unique electronic properties. However, there have been relatively few reports on the dark photocatalytic reactions utilizing organic conjugated polymers. Herein, we report the successful synthesis of an organic conjugated polymer based on poly (heptazine imide) nanocrystals (CNNCs) for H2O2 evolution and biomedical applications using a simple salt molten method and sonication–centrifugation process. The results show that these colloid CNNCs have the characteristics of photogenerated electrons accumulation and realize dark photocatalysis with high reducibility under visible light irradiation. Notably, these accumulating photogenerated electrons can reduce O2 in darkness to produce H2O2. In addition, cytotoxicity tests were conducted and it was found that H2O2 produced under dark conditions could oxidize L-arginine (L-Arg) to NO, which effectively killed tumors in the dark. This work provides an important strategy to construct organic conjugated semiconductor nanocrystals and applying them to future energy and biomedical fields. [ABSTRACT FROM AUTHOR]

PbS semiconductor nanocrystals (NCs) have been heavily explored for infrared optoelectronics but can exhibit visible-wavelength quantum-confined optical gaps when sufficiently small (⌀ = 1.8–2.7 nm). However, small PbS NCs traditionally exhibited very broad ensemble absorption linewidths, attributed to poor size-heterogeneity. Here, harnessing recent synthetic advances, we report photophysical measurements on PbS ensembles that span this underexplored size range. We observe that the smallest PbS NCs pervasively exhibit lower brightness and anomalously accelerated photoluminescence decays—relative to the idealized photophysical models that successfully describe larger NCs. We find that effects of residual ensemble size-heterogeneity are insufficient to explain our observations, so we explore plausible processes that are intrinsic to individual nanocrystals. Notably, the anomalous decay kinetics unfold, surprisingly, over hundreds-of-nanosecond timescales. These are poorly matched to effects of direct carrier trapping or fine-structure thermalization but are consistent with non-radiative recombination linked to a dynamic surface. Thus, the progressive enhancement of anomalous decay in the smallest particles supports predictions that the surface plays an outsized role in exciton–phonon coupling. We corroborate this claim by showing that the anomalous decay is significantly remedied by the installation of a rigidifying shell. Intriguingly, our measurements show that the anomalous aspect of these kinetics is insensitive to temperature between T = 298 and 77 K, offering important experimental constraint on possible mechanisms involving structural fluctuations. Thus, our findings identify and map the anomalous photoluminescence kinetics that become pervasive in the smallest PbS NCs and call for targeted experiments and theory to disentangle their origin. [ABSTRACT FROM AUTHOR]

Incorporating magnetic ions into semiconductor nanocrystals has emerged as a prominent research field for manipulating spin-related properties. The magnetic ions within the host semiconductor experience spin-exchange interactions with photogenerated carriers and are often involved in the recombination routes, stimulating special magneto-optical effects. The current account presents a comparative study, emphasizing the impact of engineering nanostructures and selecting magnetic ions in shaping carrier–magnetic ion interactions. Various host materials, including the II–VI group, halide perovskites, and I–III–VI2 in diverse structural configurations such as core/shell quantum dots, seeded nanorods, and nanoplatelets, incorporated with magnetic ions such as Mn2+, Ni2+, and Cu1+/2+ are highlighted. These materials have recently been investigated by us using state-of-the-art steady-state and transient optically detected magnetic resonance (ODMR) spectroscopy to explore individual spin-dynamics between the photogenerated carriers and magnetic ions and their dependence on morphology, location, crystal composition, and type of the magnetic ion. The information extracted from the analyses of the ODMR spectra in those studies exposes fundamental physical parameters, such as g-factors, exchange coupling constants, and hyperfine interactions, together providing insights into the nature of the carrier (electron, hole, dopant), its local surroundings (isotropic/anisotropic), and spin dynamics. The findings illuminate the importance of ODMR spectroscopy in advancing our understanding of the role of magnetic ions in semiconductor nanocrystals and offer valuable knowledge for designing magnetic materials intended for various spin-related technologies. [ABSTRACT FROM AUTHOR]

Field-effect transistors (FETs) made from colloidal quantum dot (QD) solids commonly suffer from current–voltage hysteresis caused by the bias-stress effect (BSE), which complicates fundamental studies of charge transport in QD solids and the use of QD FETs in electronics. Here, we show that the BSE can be eliminated in n-channel PbSe QD FETs by first removing the QD ligands with a dose of H2S gas and then infilling the QD films with alumina by atomic layer deposition (ALD). The H2S-treated, alumina-infilled FETs have stable, hysteresis-free device characteristics (total short-term stability), indefinite air stability (total long-term stability), and a high electron mobility of up to 14 cm2 V−1 s−1, making them attractive for QD circuitry and optoelectronic devices. The BSE-free devices are utilized to conclusively establish the dependence of the electron mobility on temperature and QD diameter. We demonstrate that the BSE in these devices is caused by both electron trapping at the QD surface and proton drift within the film. The H2S/alumina chemistry produces ligand-free PbSe/PbS/Al2O3 interfaces that lack the traps that cause the electronic part of the BSE, while full alumina infilling stops the proton motion responsible for the ionic part of the BSE. Our matrix engineering approach should aid efforts to eliminate the BSE, boost carrier mobilities, and improve charge transport in other types of nanocrystal solids. [ABSTRACT FROM AUTHOR]

Hydrophilic semiconductor quantum dots (QDs) with emission in the second near-infrared window (NIR-II) have been widely studied in bioimaging applications. In such cases, QDs are usually dispersed in water. As is known, water has strong absorbance in the NIR-II region. However, investigations on the interaction between NIR-II emitters and water molecules are ignored in previous studies. Herein, we synthesized a series of mercaptoundecanoic acid-coated silver sulfide (Ag2S/MUA) QDs with various emissions that partially or completely overlapped with the absorbance of water at 1200 nm. By constructing a hydrophobic interface of cetyltrimethylammonium bromide (CTAB) with MUA on the Ag2S QDs surface via forming an ionic bond, significant enhancement of Ag2S QDs photoluminescence (PL) intensity was observed, as well as a prolonged lifetime. These findings suggest that there is an energy transfer between Ag2S QDs and water in addition to the classical resonance absorption. Transient absorption and fluorescence spectra results revealed that the increased PL intensities and lifetime of Ag2S QDs originated from the suppressed energy transfer from Ag2S QDs to the water due to the CTAB bridged hydrophobic interfaces. This discovery is important for a deeper understanding of the photophysical mechanisms of QDs and their applications. [ABSTRACT FROM AUTHOR]

[Display omitted] Colloidal quantum dot solar cells (CQDSCs) have received great attention in the development of scalable and stable photovoltaic devices. Despite the high power-conversion-efficiency (PCE) reported, stability investigations are still limited and the exact degradation mechanisms of CQDSCs remain unclear under different atmosphere conditions. In this study, the atmospheric influence on the ZnO electron transport layer material (ETL), halide-passivated lead sulfide CQDs (PbS-PbI 2) photoactive layer material and 1,2-ethanedithiol-PbS CQDs (PbS-EDT) hole transport material on device stability in PbS CQDSCs is investigated. It was found that O 2 had negligible influence on PbS-PbI 2 , but it did induce the increase in work function of ZnO ETL and PbS-EDT layers. Notably, the increase of the ZnO work function (WF ZnO) induces the formation of interface barrier between ZnO and PbS-PbI 2 , leading to a deterioration in device efficiency. By further replacing ZnO ETL with SnO 2 , a multi-interface collaborative CQDSC was constructed to realize the PCE with high stability. This study identifies the efficiency evolution that is inherent in CQDSCs under different atmospheric conditions. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate the coherent random laser emission by combining CdSe/ZnS colloidal quantum dots with hollow optical fiber. Through the localized surface plasmon resonance induced by Ag nanoparticles (NPs), well-distinguished discrete spikes are observed from the Ag modified hollow fiber loaded with CdSe/ZnS QDs solution. In addition, coherent random laser action with low threshold is also realized in the hollow optical fiber filled with high packing-density CdSe/ZnS QDs even if the Ag NPs is not introduced. The self-assembled clusters of CdSe/ZnS QDs serve as the optical gain media as well as the strong scattering centers. The angle measurement experiments show that the directional emission of random laser can be adjusted by using different pumping manners. This facile, inexpensive, low pump threshold random laser could be widely used in photonic devices and display imaging. [ABSTRACT FROM AUTHOR]

[Display omitted] Anticancer theranostic nanocarriers have the potential to enhance the efficacy of pharmaceutical evaluation of drugs. Semiconductor nanocrystals, also known as quantum dots (QDs), are particularly promising components of drug carrier systems due to their small sizes and robust photoluminescence properties. Herein, bright CdZnSeS quantum dots were synthesized in a single step via the hot injection method. The particles have a quasi-core/shell structure as evident from the high quantum yield (85 %), which decreased to 41 % after water solubilization. These water solubilized QDs were encapsulated into gallic acid / alginate (GA-Alg) matrices to fabricate imaging QDs@mod-PAA/GA-Alg particles with enhanced stability in aqueous media. Cell viability assessments demonstrated that these nanocarriers exhibited viability ranging from 63 % to 83 % across all tested cell lines. Furthermore, the QDs@mod-PAA/GA-Alg particles were loaded with betulinic acid (BA) and ceranib-2 (C2) for in vitro drug release studies against HL-60 leukemia and PC-3 prostate cancer cells. The BA loaded QDs@mod-PAA/GA-Alg had a half-maximal inhibitory concentration (IC 50) of 8.76 μg/mL against HL-60 leukemia cells, which is 3-fold lower than that of free BA (IC 50 = 26.55 μg/mL). Similar enhancements were observed with nanocarriers loaded with C2 and simultaneously with both BA and C2. Additionally, BA:C2 loaded QDs@mod-PAA/GA-Alg nanocarriers displayed a similar enhancement (IC50 = 3.37 μg/mL compared against IC50 = 11.68 μg/mL for free BA:C2). The C2 loaded QDs@mod-PAA/GA-Alg nanocarriers had an IC50 = 2.24 μg/mL against HL-60 cells. C2 and BA loaded QDs@mod-PAA/GA-Alg NCr had IC50 values of 7.37 μg/mL and 24.55 μg/mL against PC-3 cells, respectively. [ABSTRACT FROM AUTHOR]

Photoluminescence (PL) spectroscopy of individual semiconductor nanocrystals (NCs) is a powerful method for understanding the intrinsic optical properties of these materials. Here, we report the temperature dependence of the PL spectra of single perovskite FAPbBr3 and CsPbBr3 NCs [FA = HC(NH2)2]. The temperature dependences of the PL linewidths were mainly determined by the Fröhlich interaction between excitons and longitudinal optical phonons. For FAPbBr3 NCs, a redshift in the PL peak energy appeared between 100 and 150 K, which was because of the orthorhombic-to-tetragonal phase transition. We found that the phase transition temperature of FAPbBr3 NCs decreases with decreasing NC size. [ABSTRACT FROM AUTHOR]

Semiconductor nanocrystals with an anisotropic morphology exhibit unique properties, most notably their linear polarization. The colloidal growth of semiconductor nanorods with core dots inside, also referred to as dot-in-rod (DIR) structure, has enabled the synthesis of anisotropic nanocrystals with better stability and controllable fluorescence polarization. In this study, we synthesize CdSe/CdS DIR nanocrystals, in which the position of the CdSe core particle can be controlled by using different ligand compositions during the CdS growth. Varying the core position within the DIR structure, e.g., from the center to the end of the DIR particles, results in a change in the degree of linear polarization. When the core is positioned at the center of the nanorod, the linear polarization turns out to be higher compared with tip-core DIRs. Time-resolved photoluminescence analysis reveals that the center-core DIRs have higher electron–hole interaction than tip-core DIRs because of weak uniaxial strain in center-core DIR that arises from lattice dislocations at the interface to relieve accumulated strain. [ABSTRACT FROM AUTHOR]

Intra-band transitions in colloidal quantum dots (QDs) are promising for opto-electronic applications in the mid-IR spectral region. However, such intra-band transitions are typically very broad and spectrally overlapping, making the study of individual excited states and their ultrafast dynamics very challenging. Here, we present the first full spectrum two-dimensional continuum infrared (2D CIR) spectroscopy study of intrinsically n-doped HgSe QDs, which exhibit mid-infrared intra-band transitions in their ground state. The obtained 2D CIR spectra reveal that underneath the broad absorption line shape of ∼500 cm−1, the transitions exhibit surprisingly narrow intrinsic linewidths with a homogeneous broadening of 175–250 cm−1. Furthermore, the 2D IR spectra are remarkably invariant, with no sign of spectral diffusion dynamics at waiting times up to 50 ps. Accordingly, we attribute the large static inhomogeneous broadening to the distribution of size and doping level of the QDs. In addition, the two higher-lying P-states of the QDs can be clearly identified in the 2D IR spectra along the diagonal with a cross-peak. However, there is no indication of cross-peak dynamics indicating that, despite the strong spin–orbit coupling in HgSe, transitions between the P-states must be longer than our maximum waiting time of 50 ps. This study illustrates a new frontier of 2D IR spectroscopy enabling the study of intra-band carrier dynamics in nanocrystalline materials across the entire mid-infrared spectrum. [ABSTRACT FROM AUTHOR]

As the initial synthesized colloidal quantum dots (CQDs) are generally capped with insulating ligands, ligand exchange strategies are essential in the fabrication of CQD films for solar cells, which can regulate the surface chemical states of CQDs to make them more suitable for thin‐film optoelectronic devices. However, uncontrollable surface adsorption of water molecules during the ligand exchange process introduces new defect sites, thereby impairing the resultant device performance, which attracts more efforts devoted to it but remains a puzzle. Here, we develop a solvent‐engineering‐assisted ligand exchange strategy to revamp the surface adsorption, improve the exchange efficiency, and modulate the surface chemistry for the environmentally friendly lead‐free silver bismuth disulfide (AgBiS2) CQDs. The optimized AgBiS2 CQD solar cells deliver an outstanding champion power conversion efficiency (PCE) of up to 8.95 % and improved long‐term stability. Our strategy is less environment‐dependent and can produce solar cells with negligible performance variance for several batches across several months. Our work demonstrates the critical role of solvents for ligand exchange in the surface chemistry of CQDs and the realization of high‐performance photovoltaic devices in a highly reproducible manner. [ABSTRACT FROM AUTHOR]

Colloidal semiconductor nanocrystals enable the realization and exploitation of quantum phenomena in a controlled manner, and can be scaled up for commercial uses. These materials have become important for a wide range of applications, from ultrahigh definition displays, to solar cells, quantum computing, bioimaging, optical communications, and many more. Over the last decade, lead-halide perovskite nanocrystals have rapidly gained prominence as efficient semiconductors. Although the majority of studies have focused on large nanocrystals in the weak- to intermediate-confinement regime, quantum dots (QDs) in the strongly-confined regime (with sizes smaller than the Bohr diameter, which ranges from 4–12 nm for lead-halide perovskites) offer unique opportunities, including polarized light emission and color-pure, stable luminescence in the region that is unattainable by perovskites with single-halide compositions. In this tutorial review, we bring together the latest insights into this emerging and rapidly growing area, focusing on the synthesis, steady-state optical properties (including exciton fine-structure splitting), and transient kinetics (including hot carrier cooling) of strongly-confined perovskite QDs. We also discuss recent advances in their applications, including single photon emission for quantum technologies, as well as light-emitting diodes. We finish with our perspectives on future challenges and opportunities for strongly-confined QDs, particularly around improving the control over monodispersity and stability, important fundamental questions on the photophysics, and paths forward to improve the performance of perovskite QDs in light-emitting diodes. [ABSTRACT FROM AUTHOR]

Semiconductor nanocrystals (NCs) are promising materials for various applications. Two of four recently identified CuαZnβSnγSeδ (CZTSe) domains demonstrate metallic character, while the other two exhibit semiconductor character. The presence of both metallic and semiconductor domains in one NC can hugely benefit future applications. In contrast to traditional band gap studies in the NC community, this study emphasizes that NC domain interfaces also affect the electronic properties. Specifically, the measured band gap of a tetrapod‐shaped CZTSe NC is demonstrated to originate from two specific domains (tetragonal I4¯$\bar 4$ and monoclinic P1c1 Cu2ZnSnSe4). The heterojunction between these two semiconductor domains exhibits a staggered type‐II band alignment, facilitating the separation of photogenerated electron‐hole pairs. Interestingly, tetrapod NCs have the potential to be efficient absorber materials with higher capacitance in photovoltaic applications due to the presence of both semiconductor/semiconductor interfaces and metal/semiconductor "Schottky"‐junctions. For the two photo‐absorbing domains, the calculated absorption spectra yield maximum photon‐absorption coefficients of about 105 cm−1 in the visible and UV regions and a theoretical solar power conversion efficiency up to 20.8%. These insights into the structure‐property relationships in CZTSe NCs will guide the design of more efficient advanced optical CZTSe materials for various applications. [ABSTRACT FROM AUTHOR]