Lead-free, luminescent perovskite nanocrystals obtained through ambient condition synthesis

Heterovalent substitution of toxic lead is an increasingly popular design strategy to obtain environmentally sustainable variants of the exciting material class of halide perovskites. Perovskite nanocrystals (NCs) obtained through solution-based methods exhibit exceedingly high optical quality. Unfortunately, most of these synthesis routes still require reaction under inert gas and at very high temperatures. Herein we present a novel synthesis routine for lead-free double perovskite NCs. We combine hot injection and ligand-assisted reprecipitation (LARP) methods to achieve a low-temperature and ambient atmosphere-based synthesis for manganese-doped Cs_{2}NaBiCl_{6} NCs. Mn incorporation is critical for the otherwise non-emissive material, with a 9:1 Bi:Mn precursor ratio maximizing the bright orange photoluminescence (PL) and quantum yield (QY). Higher temperatures slightly increased the material's performance, yet NCs synthesized at room temperature were still emissive, highlighting the versatility of the synthetic approach. Furthermore, the NCs show excellent long-term stability in ambient conditions, facilitating additional investigations and energy-related applications

Optical trapping and manipulation of plasmonic nanoparticles: fundamentals, applications, and perspectives

This feature article discusses the optical trapping and manipulation of plasmonic nanoparticles, an area of current interest with potential applications in nanofabrication, sensing, analytics, biology and medicine. We give an overview over the basic theoretical concepts relating to optical forces, plasmon resonances and plasmonic heating. We discuss fundamental studies of plasmonic particles in optical traps and the temperature profiles around them. We place a particular emphasis on our own work employing optically trapped plasmonic nanoparticles towards nanofabrication, manipulation of biomimetic objects and sensing

Fine‐Tuning Blue‐Emitting Halide Perovskite Nanocrystals

Lead halide perovskite nanocrystals (NCs) with narrow, bright emission in the visible range are promising candidates for light-emitting applications. Near-unity quantum yields have been realized for green and red-emitting perovskites, but efficient, stable blue-emitting perovskite materials are scarce. Current methods to synthesize quantum-confined CsPbBr3 NCs with blue emission are limited to specific wavelength ranges and still suffer from inhomogeneously broadened emission profiles. Herein, anisotropic blue-green emitting CsPbBr3 NCs are synthesized in ambient atmosphere using a spontaneous crystallization method. Optical spectroscopy reveals a gradual, asymptotic photoluminescence (PL) redshift of pristine colloidal NCs after synthesis. During this process, the emission quality improves notably as the PL spectra become narrower and more symmetric, accompanied by a PL intensity increase. Electron microscopy indicates that the gradual redshift stems from an isotropic growth of the CsPbBr3 NCs in at least two dimensions, likely due to residual precursor ions in the dispersion. Most importantly, the growth process can be halted at any point by injecting an enhancement solution containing PbBr2 and organic capping ligands. Thus, excellent control over NC size is achieved, allowing for nanometer-precise tunability of the respective emission wavelength in the range between 475 and 500 nm, enhancing the functionality of these already impressive NCs

Dark-Bright Exciton Splitting Dominates Low-Temperature Diffusion in Halide Perovskite Nanocrystal Assemblies

Semiconductor nanocrystals could replace conventional bulk materials completely in displays and light-emitting diodes. Exciton transport dominates over charge carrier transport for materials with high exciton binding energies and long ligands, such as halide perovskite nanocrystal films. Here, we investigate how beneficial superlattices - nearly perfect 3D nanocrystal assemblies of nanocrystals are to exciton transport. Surprisingly, the high degree of order is not as crucial as the individual nanocrystal size, which strongly influences the splitting of the excitonic manifold into bright and dark states. At very low temperatures, the energetic splitting is large for the smallest nanocrystals, and dark levels with low oscillator strength effectively trap excitons inside individual nanocrystals, suppressing diffusion. The effect is reversed at elevated temperatures, and the larger NC size becomes detrimental to exciton transport due to enhanced exciton trapping and dissociation. Our results reveal that the nanocrystal size must be strongly accounted for in design strategies of future optoelectronic applications

Constructing and Compressing Global Moment Descriptors from Local Atomic Environments

Local atomic environment descriptors (LAEDs) are used in the materials science and chemistry communities, for example, for the development of machine learning interatomic potentials. Despite the fact that LAEDs have been extensively studied and benchmarked for various applications, global structure descriptors (GSDs), i.e., descriptors for entire molecules or crystal structures, have been mostly developed independently based on other approaches. Here, we propose a systematically improvable methodology for constructing a space of representations of GSDs from LAEDs by incorporating statistical information and information about chemical elements. We apply the method to construct GSDs of varying complexity for lithium thiophosphate structures that are of interest as solid electrolytes and use an information-theoretic approach to obtain an optimally compressed GSD. Finally, we report the performance of the compressed GSD for energy prediction tasks

Doubly stabilized perovskite nanocrystal luminescence downconverters

Halide perovskite nanocrystals (NCs) have emerged as a promising material for applications ranging from light-emitting diodes (LEDs) to solar cells and photodetectors. Still, several issues impede the realization of the nanocrystals' full potential, most notably their susceptibility to degradation from environmental stress. This work demonstrates highly stable perovskite nanocrystals (NCs) with quantum yields as high as 95 % by exploiting a ligand-assisted copolymer nanoreactor-based synthesis. The organic ligands thereby serve a dual function by enhancing the uptake of precursors and passivating the NCs. The polymer micelles and ligands thus form a double protection system, shielding the encapsulated NCs from water-, heat- and UV-light-induced degradation. We demonstrate the optoelectronic integrability by incorporating the perovskite NCs as spectrally pure downconverters on top of a deep-blue-emitting organic LED. These results establish a way of stabilizing perovskite NCs for optoelectronics while retaining their excellent optical properties

High‐Performance Monolayer MoS 2 Field‐Effect Transistors on Cyclic Olefin Copolymer‐Passivated SiO 2 Gate Dielectric

Abstract Trap states of the semiconductor/gate dielectric interface give rise to a pronounced subthreshold behavior in field‐effect transistors (FETs) diminishing and masking intrinsic properties of 2D materials. To reduce the well‐known detrimental effect of SiO 2 surface traps, this work spin‐coated an ultrathin (≈5 nm) cyclic olefin copolymer (COC) layer onto the oxide and this hydrophobic layer acts as a surface passivator. The chemical resistance of COC allows to fabricate monolayer MoS 2 FETs on SiO 2 by standard cleanroom processes. This way, the interface trap density is lowered and stabilized almost fivefold, to around 5 × 10 11 cm −2 eV −1 , which enables low‐voltage FETs even on 300 nm thick SiO 2 . In addition to this superior electrical performance, the photoresponsivity of the MoS 2 devices on passivated oxide is also enhanced by four orders of magnitude compared to nonpassivated MoS 2 FETs. Under these conditions, negative photoconductivity and a photoresponsivity of 3 × 10 7 A W −1 is observed which is a new highest value for MoS 2 . These findings indicate that the ultrathin COC passivation of the gate dielectric enables to probe exciting properties of the atomically thin 2D semiconductor, rather than interface trap dominated effects.High‐performance monolayer MoS 2 ‐based electronic and optoelectronic devices are fabricated on SiO 2 gate dielectric passivated with cyclic olefin copolymer. The passivation eliminates the interaction with interface trap states which are detrimental for the electronic and optoelectronic performance of the devices. imag

Strong coupling effects in hybrid plexitonic systems

Trabajo presentado a la 3rd International Conference on Applications of Optics and Photonics, celebrado en Faro (Portugal) del 8 al 12 de mayo de 2017.We investigated the interactions between localized plasmons in gold nanorods and excitons in J-aggregates and were able to track an anticrossing behavior of the hybridized modes both in the extinction and in the photoluminescence spectra of this hybrid system. We identified the nonlinear optical behavior of this system by transient absorption spectroscopy. Finally using magnetic circular dichroism spectroscopy we showed that nonmagnetic organic molecules exhibit magneto-optical response due to binding to a plasmonic nanoparticles. In our experiments we also studied the effect of detuning as well as the effect of off- and on resonance excitation on the hybrid states.We acknowledge financial support from Project Fis2016.80174-P (PLASMOQUANTA) from MINECO (Ministerio de Economía y Competitividad). L.L.-M. acknowledges funding from the European Research Council (ERC Advanced Grant 267867, Plasmaquo). This study was supported by the Ministry of Education and Science of the Russian Federation, grant no. 14.Y26.31.0011.Peer Reviewe

GWpy: A Python package for gravitational-wave astrophysics

GWpy is a Python software package that provides an intuitive, object-oriented interface through which to access, process, and visualise data from gravitational-wave detectors. GWpy provides a number of new utilities for studying data, as well as an improved user interface for a number of existing tools. The ease-of-use, along with extensive online documentation and examples, has resulted in widespread adoption of GWpy as a basis for Python software development in the international gravitational-wave community