The First Decade of Colloidal Lead Halide Perovskite Quantum Dots (in our Laboratory).

Ten years after the discovery of colloidal lead halide perovskite nanocrystals (LHP NCs), the field has witnessed substantial progress in synthetic methods, understanding of their surface chemistry and unique optical properties, precise control over NC size, shape, and composition. Ligand engineering, particularly with cationic and zwitterionic head groups, massively enhanced NC stability, compatibility with organic solvents, and photoluminescence efficiency. These breakthroughs allowed for the self-assembly of monodisperse NCs into complex long-range ordered superlattices and enabled the exploration of collective optical phenomena, such as superfluorescence.

Size-Dependent Multiexciton Dynamics Governs Scintillation From Perovskite Quantum Dots.

The recent emergence of quantum-confined nanomaterials in the field of radiation detection, in particular lead halide perovskite nanocrystals, offers scalability and performance advantages over conventional materials. This development raises fundamental questions about the mechanism of scintillation itself at the nanoscale and the role of particle size, arguably the most defining parameter of quantum dots. Understanding this is crucial for the design and optimization of future nanotechnology scintillators.

Quantitative photocurrent scanning probe microscopy on PbS quantum dot monolayers.

Photoconductive atomic force microscopy can probe monolayers of PbS/perovskite quantum dots (QDs) with a contact area of 1-3 QDs in stable and reproducible acquisition conditions for / curves and photocurrent maps. From the measurements, quantitative values for the barrier height, built-in voltage, diffusion constant and ideality factor are deduced with high precision. The data analysis is based on modelling a superposition of the drift current of the photo-excited charges and a diffusion current across the interface barriers, providing physical insight into the underlying processes.

AFM-IR of Electrohydrodynamically Printed PbS Quantum Dots: Quantifying Ligand Exchange at the Nanoscale.

Colloidal quantum dots (cQDs), semiconductor materials with widely tunable properties, can be printed in submicrometer patterns through electrohydrodynamic printing, avoiding aggressive photolithography steps. Postprinting ligand exchange determines the final optoelectronic properties of the cQD structures. However, achieving a complete bulk exchange is challenging, and the conventional vibrational analysis lacks the required spatial resolution.

Highly-Polarized Emission Provided by Giant Optical Orientation of Exciton Spins in Lead Halide Perovskite Crystals.

Quantum technologic and spintronic applications require reliable material platforms that enable significant and long-living spin polarization of excitations, the ability to manipulate it optically in external fields, and the possibility to implement quantum correlations between spins, i.e., entanglement.

Intraband Cooling and Auger Recombination in Weakly to Strongly Quantum-Confined CsPbBr Perovskite Nanocrystals.

Semiconductor nanocrystals (NCs) with size-tuned energy gaps present unique and desirable properties for optoelectronic applications. Recent synthetic advancements offer routes to spheroidal CsPbBr perovskite NCs in the strong quantum confinement regime with narrow size dispersion. Using tunable femtosecond laser pulses, we examine intraband carrier relaxation using transient absorption spectroscopy and show that, across the transition from weak to strong confinement, hot carrier lifetime increases compared to larger bulk-like particles.

Quantifying Förster Resonance Energy Transfer from Single Perovskite Quantum Dots to Organic Dyes.

Colloidal quantum dots (QDs) are promising regenerable photoredox catalysts offering broadly tunable redox potentials along with high absorption coefficients. QDs have thus far been examined for various organic transformations, water splitting, and CO reduction. Vast opportunities emerge from coupling QDs with other homogeneous catalysts, such as transition metal complexes or organic dyes, into hybrid nanoassemblies exploiting energy transfer (ET), leveraging a large absorption cross-section of QDs and long-lived triplet states of cocatalysts.

Coherent Carrier Spin Dynamics in FAPbBr Perovskite Crystals.

Coherent spin dynamics of electrons and holes are studied in hybrid organic-inorganic lead halide perovskite FAPbBr bulk single crystals using the time-resolved Kerr ellipticity technique at cryogenic temperatures. The Larmor spin precession of the carrier spins in a magnetic field is monitored to measure the Landé -factors of electrons (+2.44) and holes (+0.

Strong Light-Matter Coupling in Lead Halide Perovskite Quantum Dot Solids.

Strong coupling between lead halide perovskite materials and optical resonators enables both polaritonic control of the photophysical properties of these emerging semiconductors and the observation of fundamental physical phenomena. However, the difficulty in achieving optical-quality perovskite quantum dot (PQD) films showing well-defined excitonic transitions has prevented the study of strong light-matter coupling in these materials, central to the field of optoelectronics. Herein we demonstrate the formation at room temperature of multiple cavity exciton-polaritons in metallic resonators embedding highly transparent Cesium Lead Bromide quantum dot (CsPbBr-QD) solids, revealed by a significant reconfiguration of the absorption and emission properties of the system.

Single-photon superradiance in individual caesium lead halide quantum dots.

The brightness of an emitter is ultimately described by Fermi's golden rule, with a radiative rate proportional to its oscillator strength times the local density of photonic states. As the oscillator strength is an intrinsic material property, the quest for ever brighter emission has relied on the local density of photonic states engineering, using dielectric or plasmonic resonators. By contrast, a much less explored avenue is to boost the oscillator strength, and hence the emission rate, using a collective behaviour termed superradiance.

Designer phospholipid capping ligands for soft metal halide nanocrystals.

The success of colloidal semiconductor nanocrystals (NCs) in science and optoelectronics is inextricable from their surfaces. The functionalization of lead halide perovskite NCs poses a formidable challenge because of their structural lability, unlike the well-established covalent ligand capping of conventional semiconductor NCs. We posited that the vast and facile molecular engineering of phospholipids as zwitterionic surfactants can deliver highly customized surface chemistries for metal halide NCs.

Hot Excitons Cool in Metal Halide Perovskite Nanocrystals as Fast as CdSe Nanocrystals.

The idea of phonon bottlenecks has long been pursued in nanoscale materials for their application in hot exciton devices, such as photovoltaics. Decades ago, it was shown that there is no quantum phonon bottleneck in strongly confined quantum dots due to their physics of quantum confinement. More recently, it was proposed that there are hot phonon bottlenecks in metal halide perovskites due to their physics.

Synthesis of Antimicrobial Gallium Nanoparticles Using the Hot Injection Method.

Antibiotic resistance continues to be an ongoing problem in global public health despite interventions to reduce antibiotic overuse. Furthermore, it threatens to undo the achievements and progress of modern medicine. To address these issues, the development of new alternative treatments is needed.

Enhancing Multiexcitonic Emission in Metal-Halide Perovskites by Quantum Confinement.

Semiconductor metal halide perovskite nanocrystals have been under intense investigation for their promise in a variety of optoelectronic applications, which arises from their remarkable properties of defect tolerance and efficient light emission. Recently, quantum dot versions of perovskite nanocrystals have been available, enabling investigation of how quantum size effects control optical function and performance in these quantum dots (QD), past their well-known covalent II-VI analogues. We perform time-resolved photoluminescence (t-PL) experiments on CsPbBr perovskite nanocrystals spanning in diameter from 5.

Weak Dispersion of Exciton Landé Factor with Band Gap Energy in Lead Halide Perovskites: Approximate Compensation of the Electron and Hole Dependences.

The optical properties of lead halide perovskite semiconductors in vicinity of the bandgap are controlled by excitons, so that investigation of their fundamental properties is of critical importance. The exciton Landé or g-factor g is the key parameter, determining the exciton Zeeman spin splitting in magnetic fields. The exciton, electron, and hole carrier g-factors provide information on the band structure, including its anisotropy, and the parameters contributing to the electron and hole effective masses.

Colloidal CsPbX Nanocrystals with Thin Metal Oxide Gel Coatings.

Lead halide perovskite (LHP) nanocrystals (NCs) have gathered much attention as light-emitting materials, particularly owing to their excellent color purity, band gap tunability, high photoluminescence quantum yield (PLQY), low cost, and scalable synthesis. To enhance the stability of LHP NCs, bulky strongly bound organic ligands are commonly employed, which counteract the extraction of charge carriers from the NCs and hinder their use as photoconductive materials and photocatalysts. Replacing these ligands with a thin coating is a complex challenge due to the highly dynamic ionic lattice, which is vulnerable to the commonly employed coating precursors and solvents.

Intrinsic Formamidinium Tin Iodide Nanocrystals by Suppressing the Sn(IV) Impurities.

The long search for nontoxic alternatives to lead halide perovskites (LHPs) has shown that some compelling properties of LHPs, such as low effective masses of carriers, can only be attained in their closest Sn(II) and Ge(II) analogues, despite their tendency toward oxidation. Judicious choice of chemistry allowed formamidinium tin iodide (FASnI) to reach a power conversion efficiency of 14.81% in photovoltaic devices.

Many-Body Correlations and Exciton Complexes in CsPbBr Quantum Dots.

All-inorganic lead-halide perovskite (LHP) (CsPbX , X = Cl, Br, I) quantum dots (QDs) have emerged as a competitive platform for classical light-emitting devices (in the weak light-matter interaction regime, e.g., LEDs and laser), as well as for devices exploiting strong light-matter interaction at room temperature.

Photoconductivity of PbS/perovskite quantum dots in gold nanogaps.

We demonstrate that the photoconductance of colloidal PbS/MAPbI quantum dots in nanoscale gold electrode gaps shows a consistent power law dependence of the photocurrent on the light intensity with an exponent slightly below 0.7. The gap sizes are between 25 and 800 nm and by scanning photocurrent microscopy we evidence the strong localization and high reproducibility of photocurrent generation.

Controlling the nucleation and growth kinetics of lead halide perovskite quantum dots.

Colloidal lead halide perovskite nanocrystals are of interest as photoluminescent quantum dots (QDs) whose properties depend on the size and shape. They are normally synthesized on subsecond time scales through hard-to-control ionic metathesis reactions. We report a room-temperature synthesis of monodisperse, isolable, spheroidal APbBr QDs ("A" indicates cesium, formamidinium, and methylammonium) that are size tunable from 3 to >13 nanometers.

Ligands Mediate Anion Exchange between Colloidal Lead-Halide Perovskite Nanocrystals.

The soft lattice of lead-halide perovskite nanocrystals (NCs) allows tuning their optoelectronic characteristics via anion exchange by introducing halide salts to a solution of perovskite NCs. Similarly, cross-anion exchange can occur upon mixing NCs of different perovskite halides. This process, though, is detrimental for applications requiring perovskite NCs with different halides in close proximity.

Room-Temperature, Highly Pure Single-Photon Sources from All-Inorganic Lead Halide Perovskite Quantum Dots.

Attaining pure single-photon emission is key for many quantum technologies, from optical quantum computing to quantum key distribution and quantum imaging. The past 20 years have seen the development of several solid-state quantum emitters, but most of them require highly sophisticated techniques (e.g.

Nanoscale-Resolved Surface-to-Bulk Electron Transport in CsPbBr Perovskite.

Describing the nanoscale charge carrier transport at surfaces and interfaces is fundamental for designing high-performance optoelectronic devices. To achieve this, we employ time- and angle-resolved photoelectron spectroscopy with ultraviolet pump and extreme ultraviolet probe pulses. The resulting high surface sensitivity reveals an ultrafast carrier population decay associated with surface-to-bulk transport, which was tracked with a sub-nanometer spatial resolution normal to the surface, and on a femtosecond time scale, in the case of the inorganic CsPbBr lead halide perovskite.

Lead-Dominated Hyperfine Interaction Impacting the Carrier Spin Dynamics in Halide Perovskites.

The outstanding optical quality of lead halide perovskites inspires studies of their potential for the optical control of carrier spins as pursued in other materials. Entering largely uncharted territory, time-resolved pump-probe Kerr rotation is used to explore the coherent spin dynamics of electrons and holes in bulk formamidinium caesium lead iodine bromide (FA Cs PbI Br ) and to determine key parameters characterizing interactions of their spins, such as the g-factors and relaxation times. The demonstrated long spin dynamics and narrow g-factor distribution prove the perovskites as promising competitors for conventional semiconductors in spintronics.