Single-photon superabsorption in CsPbBr perovskite quantum dots.

The absorption of light via interband optical transitions plays a key role in nature and applied technology, enabling efficient photosynthesis and photovoltaic cells, fast photodetectors or sensitive (quantum) light-matter interfaces. In many such photonic systems, enhancing the light absorption strength would be beneficial for yielding higher device efficiency and enhanced speed or sensitivity. So far, however, cavity-free light absorbers feature poorly engineerable absorption rates, consistent with the notion that the coupling strength between the initial and final states is an intrinsic material parameter.

Coherent Multi-Dimensional Spectroscopy Reveals Homogeneous Lineshape Dynamics in CsPbBr Quantum Dots.

Lead halide perovskite (LHP) quantum dots (QD) are an attractive material for light emissive applications due to their lattice, which is both dynamically disordered and defect tolerant. The development of LHP QD for quantum emitters critically depends on the characterization of their homogeneous lineshapes. Homogeneous lineshapes are measured by single dot photoluminescence spectroscopy only at cryogenic temperatures for which their lattice dynamics are frozen out.

Reply to "Comment on 'Intrinsic Formamidinium Tin Iodide Nanocrystals by Suppressing the Sn(IV) Impurities'".

In this reply, we address the comments of A. Dhingra on our prior work titled "Intrinsic Formamidinium Tin Iodide Nanocrystals by Suppressing the Sn(IV) Impurities".

Room-temperature cavity exciton-polariton condensation in perovskite quantum dots.

The exploitation of the strong light-matter coupling regime and exciton-polariton condensates has emerged as a compelling approach to introduce strong interactions and nonlinearities into numerous photonic applications. The use of colloidal semiconductor quantum dots with strong three-dimensional confinement as the active material in optical microcavities would be highly advantageous due to their versatile structural and compositional tunability and wet-chemical processability, as well as potentially enhanced, confinement-induced polaritonic interactions. Yet, to date, exciton-polariton condensation in a microcavity has neither been achieved with epitaxial nor with colloidal quantum dots.

Correlated Lattice Fluctuations in CsPbBr Quantum Dots Give Rise to Long-Lived Electronic Coherence.

Electronic coherence is central to numerous areas of science, from quantum biology to quantum materials. In quantum materials, lead-halide perovskite (LHP) quantum dots (QDs) have been shown to support electronic coherence through observation of coherent single-photon emission and superfluorescence arising from spatial coherence at low temperatures. In contrast, direct measurement of temporal coherence between exciton states has been lacking.

Dependence of Exciton Spin Dynamics on Quantum Confinement Dimensionality in CsPbBr Nanocrystals.

Semiconductor nanomaterials offer a promising platform to produce optically addressable spins for use in quantum technologies. Here, we examine CsPbBr nanospheres, cubes, and rods spanning the zero-dimensional (0D) to three-dimensional (3D) transition to investigate the influence of dimensionality and shape on exciton spin decoherence. Using circularly polarized transient absorption spectroscopy, we find that the spin relaxation rate is independent of the surface to volume ratio and instead follows a dependence on the length of the shortest dimension.

Coherent Multidimensional Spectroscopy Reveals Hot Exciton Cooling Landscapes in CsPbBr Quantum Dots.

Hot exciton relaxation dynamics is one of the main processes in quantum dots (QD), conferring their functions in optoelectronic devices spanning photovoltaics and solar fuel generation to light emitting diodes, lasers, and quantum light sources. The challenge has been to monitor energy relaxation dynamics in parallel with resolution of excitation or excess energy. Here, we exploit the unique capacity of Coherent Multi-Dimensional Spectroscopy (CMDS) to provide the first observation of the hot exciton cooling landscape of a large size range of CsPbBr lead halide perovskite QD, notable for their impact on optoelectronic devices, as well as their strong and unique exciton-lattice coupling.

Room Temperature Superfluorescence from an Electron-Hole Liquid.

Superfluorescence, a coherent burst of light from an excited ensemble of emitters, is a crucial quantum optical phenomenon with far-reaching implications in nanophotonics and many-body optical processes. Despite its observation in various systems, realizing superfluorescence in an electron-hole plasma (EHP) at room temperature has remained a formidable challenge, hindering the development of continuous-wave and electrically excited superfluorescence devices. Herein, we address this challenge by condensing the high-density EHP into an electron-hole liquid (EHL) at room temperature, thereby preserving quantum coherence.

Ligand Influence on the Performance of Cesium Lead Bromide Perovskite Quantum Dots in Photocatalytic C(sp)-H Bromination Reactions.

Lead halide perovskite quantum dots (LHP QDs) CsPbX generate immense interest as narrow-band emitters for displays, lasers, and quantum light sources. All QD applications rely on suited engineering of surface capping ligands. The first generation of LHP QDs employed oleic acid/oleyl amine capping and have found only a limited use in photoredox catalysis.

Effect of Crystal Symmetry of Lead Halide Perovskites on the Optical Orientation of Excitons.

The great variety of lead halide perovskite semiconductors represents an outstanding platform for studying crystal symmetry effects on the spin-dependent properties. Access to them is granted through the optical orientation of exciton and carrier spins by circularly polarized photons. Here, the exciton spin polarization is investigated at 1.

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.

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.