CAT: A Compound Attachment Tool for the Construction of Composite Chemical Compounds.

The continuous improvement of computer architectures allows for the simulation of molecular systems of growing sizes. However, such calculations still require the input of initial structures, which are also becoming increasingly complex. In this work, we present CAT, a Compound Attachment Tool (source code available at https://github.

Alloying Bi-Doped CsAgNaInCl Nanocrystals with K Cations Modulates Surface Ligands Density and Photoluminescence Efficiency.

We show how, in the synthesis of yellow-emissive Bi-doped CsAgNaInCl double perovskite nanocrystals (NCs), preventing the transient formation of Ag particles increases the photoluminescence quantum yield (PLQY) of the NCs from ∼30% to ∼60%. Calculations indicate that the presence of even a single Ag species on the surface of a NC introduces deep trap states. The PL efficiency of these NCs is further increased to ∼70% by partial replacement of Na with K ions, up to a 7% K content, due to a lattice expansion that promotes a more favorable ligands packing on the NC surface, hence better surface passivation.

Cu → Mn Energy Transfer in Cu, Mn Coalloyed CsZnCl Colloidal Nanocrystals.

In this work, we report the hot-injection synthesis of CsZnCl colloidal nanocrystals (NCs) with tunable amounts of Cu and Mn substituent cations. All the samples had a rodlike morphology, with a diameter of ∼14 nm and a length of ∼30-100 nm. Alloying did not alter the crystal structure of the host CsZnCl NCs, and Cu ions were mainly introduced in the oxidation state +1 according to X-ray photoelectron and electron paramagnetic resonance spectroscopies.

Halide perovskites as disposable epitaxial templates for the phase-selective synthesis of lead sulfochloride nanocrystals.

Colloidal chemistry grants access to a wealth of materials through simple and mild reactions. However, even few elements can combine in a variety of stoichiometries and structures, potentially resulting in impurities or even wrong products. Similar issues have been long addressed in organic chemistry by using reaction-directing groups, that are added to a substrate to promote a specific product and are later removed.

Cesium Manganese Bromide Nanocrystal Sensitizers for Broadband Vis-to-NIR Downshifting.

Simultaneously achieving both broad absorption and sharp emission in the near-infrared (NIR) is challenging. Coupling of an efficient absorber such as lead halide perovskites to lanthanide emissive species is a promising way to meet the demands for visible-to-NIR spectral conversion. However, lead-based perovskite sensitizers suffer from relatively narrow absorption in the visible range, poor stability, and toxicity.

The Reactivity of CsPbBr Nanocrystals toward Acid/Base Ligands.

The interaction of lead bromide perovskite nanocrystals with charged ligands, such as salts, zwitterions, or acid-base pairs, has been extensively documented over the past few years. On the other hand, little is known about the reactivity of perovskite nanocrystals toward neutral ligands. To fill this gap, in this work we study the interaction of CsPbBr nanocrystals passivated with didodecyldimethylammonium bromide (DDABr) toward a series of exogenous acid/base ligands using a combined computational and experimental approach.

Sb-Doped Metal Halide Nanocrystals: A 0D versus 3D Comparison.

We synthesize colloidal nanocrystals (NCs) of RbInCl, composed of isolated metal halide octahedra ("0D"), and of CsNaInCl and CsKInCl double perovskites, where all octahedra share corners and are interconnected ("3D"), with the aim to elucidate and compare their optical features once doped with Sb ions. Our optical and computational analyses evidence that the photoluminescence quantum yield (PLQY) of all these systems is consistently lower than that of the corresponding bulk materials due to the presence of deep surface traps from under-coordinated halide ions. Also, Sb-doped "0D" RbInCl NCs exhibit a higher PLQY than Sb-doped "3D" CsNaInCl and CsKInCl NCs, most likely because excitons responsible for the PL emission migrate to the surface faster in 3D NCs than in 0D NCs.

An Overview of Computational Studies on Colloidal Semiconductor Nanocrystals.

In the last two decades, colloidal semiconductor nanocrystals have emerged as a phenomenal research topic due to their size-dependent optoelectronic properties and to their outstanding versatility in many technological applications. In this review, we provide an historical account of the most relevant computational works that have been carried out to understand atomistically the electronic structure of these materials, including the main requirements needed for the preparation of nanocrystal models that align well with the experiments. We further discuss how the advancement of these computational tools has affected the analysis of these nanomaterials over the years.

Colloidal Bi-Doped CsAg Na InCl Nanocrystals: Undercoordinated Surface Cl Ions Limit their Light Emission Efficiency.

Understanding and tuning the ligand shell composition in colloidal halide perovskite nanocrystals (NCs) has been done systematically only for Pb-based perovskites, while much less is known on the surface of Pb-free perovskite systems. Here, we reveal the ligand shell architecture of Bi-doped CsAg Na InClNCs via nuclear magnetic resonance analysis. This material, in its bulk form, was found to have a photoluminescence quantum yield (PLQY) as high as 86%, a record value for halide double perovskites.

The Future of Ligand Engineering in Colloidal Semiconductor Nanocrystals.

Next-generation colloidal semiconductor nanocrystals featuring enhanced optoelectronic properties and processability are expected to arise from complete mastering of the nanocrystals' surface characteristics, attained by a rational engineering of the passivating ligands. This aspect is highly challenging, as it underlies a detailed understanding of the critical chemical processes that occur at the nanocrystal-ligand-solvent interface, a task that is prohibitive because of the limited number of nanocrystal syntheses that could be tried in the lab, where only a few dozen of the commercially available starting ligands can actually be explored. However, this challenging goal can be addressed nowadays by combining experiments with atomistic calculations and machine learning algorithms.

Halide Perovskite-Lead Chalcohalide Nanocrystal Heterostructures.

We report the synthesis of colloidal CsPbX-PbSBr (X = Cl, Br, I) nanocrystal heterostructures, providing an example of a sharp and atomically resolved epitaxial interface between a metal halide perovskite and a non-perovskite lattice. The CsPbBr-PbSBr nanocrystals are prepared by a two-step direct synthesis using preformed subnanometer CsPbBr clusters. Density functional theory calculations indicate the creation of a quasi-type II alignment at the heterointerface as well as the formation of localized trap states, promoting ultrafast separation of photogenerated excitons and carrier trapping, as confirmed by spectroscopic experiments.

Compositional Tuning of Carrier Dynamics in CsNa Ag BiCl Double-Perovskite Nanocrystals.

We devised a hot-injection synthesis to prepare colloidal double-perovskite CsNaBiCl nanocrystals (NCs). We also examined the effects of replacing Na with Ag cations by preparing and characterizing CsNa Ag BiCl alloy NCs with ranging from 0 to 1. Whereas CsNaBiCl NCs were not emissive, CsNa Ag BiCl NCs featured a broad photoluminescence band at ∼690 nm, Stokes-shifted from the respective absorption by ≥1.

Nanocrystals of Lead Chalcohalides: A Series of Kinetically Trapped Metastable Nanostructures.

We report the colloidal synthesis of a series of surfactant-stabilized lead chalcohalide nanocrystals. Our work is mainly focused on PbSBr, a chalcohalide phase unknown to date that does not belong to the ambient-pressure PbS-PbBr phase diagram. The PbSBr nanocrystals herein feature a remarkably narrow size distribution (with a size dispersion as low as 5%), a good size tunability (from 7 to ∼30 nm), an indirect bandgap, photoconductivity (responsivity = 4 ± 1 mA/W), and stability for months in air.