Iatrogenic or recurrent bladder neck contracture treated by the Palminteri-Ferrari technique: a new way to approach a frustrating condition.

PURPOSE: Bladder neck stricture (BNS) is a bothersome disease which may affect patients after trauma or prostatic surgery. It is frustrating due to the low durable success rate of currently available surgical techniques. The aim of the study is to explore the efficacy of a novel technique. MATERIALS & METHODS: The surgical protocol was developed by two high case-volume surgeons. The technique consists of Holmium laser incisions at 3-6-9-12 o'clock. Subsequently, triamcinolone acetonide 40 mg is injected. Two months later, the BNS is endoscopically checked in operatory room and re-procedure take place, if necessary (max 3 times). Failure was defined as the need of definitive urinary diversion. Subjective satisfaction was measured through PGI-I Questionnaire. RESULTS: A total of 45 patients were enrolled. Median age was 63 (IQR 59-69) years and BNS developed by different causes. Naïve BNS procedure patients were 12 (26.7%), others 33 (73.3%) underwent median 2 (IQR 1-4) previous urethrotomies, including 16 other surgeries. Suprapubic bladder catheter was present in 34 patients (75.6%). No complications were registered. Re-procedure at control was necessary in 24 patients (53.3%) for a median of 1 (IQR 1-3) procedures. At median follow-up of 18 months, failures were 4 (8.9%) and urinary incontinence was reported in 2 patients (4.5%) who required incontinence surgery. Median PGI-I was 2. CONCLUSIONS: Our technique of BNS treatment allows good outcomes and high rate of subjective improvement amongst patients. Moreover, naïve patients seem to have better results. However, longer follow-up and higher sample size are mandatory to further assess these data.

Small intestinal submucosa graft bulbar urethroplasty is a viable technique: results compared to buccal mucosa graft urethroplasty after propensity score matching.

PURPOSE: Small intestinal submucosa (SIS) graft urethroplasty has been employed to decrease buccal mucosa morbidity and facilitate the procedure. The first published series had a short follow-up, inhomogeneous patient selection, and a lack of a control group. Our purpose is to report treatment outcomes at 13 years in a propensity score-matched cohort comparing bulbar urethroplasty with SIS (SISU) or buccal mucosa (BMU). METHODS: From our institutional database of 1132 bulbar urethroplasties, we used propensity score matching with the nearest-neighbor method without replacement to generate a study sample of 25 BMU and 25 SISU. Failure was defined as any treatment after urethroplasty. Survival analyses were used to analyze treatment failure occurrence with data censored at 156mo. RESULTS: Matching resulted in a complete correction of bias between the two samples except for the follow-up duration, which was slightly longer in the SIS group. The cumulative treatment success probability of BMU and SISU at 156mo was 83.4% and 68%, respectively. At multivariable Cox regression, SIS graft, previous urethrotomy, stricture length, and lower postoperative Qmax (within 2mo after catheter removal) were predictors of failure. Stricture length had a more remarkable effect in SISU, with estimated survival probabilities from the Cox model lower than 80% in strictures > = 3 cm. CONCLUSION: SIS has poorer outcomes compared to BM but may still be useful when BM grafting is not possible. The best candidates for SISU, with similar success to BMU, are patients with strictures shorter than 3 cm, preferably without a history of DVIU.

Is water vapor thermal therapy safe and feasible in elderly and frail men? The Italian experience.

PURPOSE: In recent years, water vapor thermal therapy (WVTT) has spread as minimally invasive technique in lower urinary tract symptoms due to benign prostatic hyperplasia treatment. Even if its safety and feasibility have been largely proved in young men, nobody has proved the same feasibility and safety in the elderly (men older than 75 years old). Our aim is to compare WVTT safety outcomes in men older than 75 with younger men. METHODS: We prospectively collected data on men who underwent water vapor thermal therapy from 2019. We compared data on operative time, number of injections, intra-operative and post-operative complications, reinterventions rate. RESULTS: We enrolled 426 patients; among these, 60 were older than 75 years old, 366 were younger. Our cohorts of patients had similar results in terms of intra-operative and post-operative complications. Operative time accounts about 11 min for both groups (p = 0.535), total number of injections was seven for young men and eight for elderly (p = 0.314). We found no intra-operative complications in elderly men group and only one in the younger group (p = 0.678), while five younger men underwent clot retention, and two elderly men experienced this complication (p = 0.239). Only one transfusion occurred in the elderly group. No differences between groups occurred in terms of length of stay, post-operative urinary retention and reintervention rate, while catheterization time was longer in the elderly men. CONCLUSION: WVTT is a safe procedure in elderly patients with comparable intra-operative and post-operative complication rate in comparison with younger patients.

Towards the extraction of the crystal cell parameters from pair distribution function profiles.

The approach based on atomic pair distribution function (PDF) has revolutionized structural investigations by X-ray/electron diffraction of nano or quasi-amorphous materials, opening up the possibility of exploring short-range order. However, the ab initio crystal structural solution by the PDF is far from being achieved due to the difficulty in determining the crystallographic properties of the unit cell. A method for estimating the crystal cell parameters directly from a PDF profile is presented, which is composed of two steps: first, the type of crystal cell is inferred using machine-learning approaches applied to the PDF profile; second, the crystal cell parameters are extracted by means of multivariate analysis combined with vector superposition techniques. The procedure has been validated on a large number of PDF profiles calculated from known crystal structures and on a small number of measured PDF profiles. The lattice determination step has been benchmarked by a comprehensive exploration of different classifiers and different input data. The highest performance is obtained using the k-nearest neighbours classifier applied to whole PDF profiles. Descriptors calculated from the PDF profiles by recurrence quantitative analysis produce results that can be interpreted in terms of PDF properties, and the significance of each descriptor in determining the prediction is evaluated. The cell parameter extraction step depends on the cell metric rather than its type. Monometric, dimetric and trimetric cells have top-1 estimates that are correct 40, 20 and 5% of the time, respectively. Promising results were obtained when analysing real nanocrystals, where unit cells close to the true ones are found within the top-1 ranked solution in the case of monometric cells and within the top-6 ranked solutions in the case of dimetric cells, even in the presence of a crystalline impurity with a weight fraction up to 40%.

CsPbCl3 → CsPbI3 Exchange in Perovskite Nanocrystals Proceeds through a Jump-the-Gap Reaction Mechanism.

Halide exchange is a popular strategy to tune the properties of CsPbX3 nanocrystals after synthesis. However, while Cl → Br and Br → I exchanges proceed through the formation of stable mixed-halide nanocrystals, the Cl ⇌ I exchange is more elusive. Indeed, the large size difference between chloride and iodide ions causes a miscibility gap in the CsPbCl3-CsPbI3 system, preventing the isolation of stable CsPb(ClxI1-x)3 nanocrystals. Yet, previous works have claimed that a full CsPbCl3 → CsPbI3 exchange can be achieved. Even more interestingly, interrupting the exchange prematurely yields a mixture of CsPbCl3 and CsPbI3 nanocrystals that coexist without undergoing further transformation. Here, we investigate the reaction mechanism of CsPbCl3 → CsPbI3 exchange in nanocrystals. We show that the reaction proceeds through the early formation of iodide-doped CsPbCl3 nanocrystals covered by a monolayer shell of CsI. These nanocrystals then leap over the miscibility gap between CsPbCl3 and CsPbI3 by briefly transitioning to short-lived and nonrecoverable CsPb(ClxI1-x)3 nanocrystals, which quickly expel the excess chloride and turn into the chloride-doped CsPbI3 nanocrystals found in the final product.

Nucleation and Growth of Bipyramidal Yb:LiYF4 Nanocrystals-Growing Up in a Hot Environment.

Lanthanide-doped LiYF4 (Ln:YLF) is commonly used for a broad variety of optical applications, such as lasing, photon upconversion and optical refrigeration. When synthesized as nanocrystals (NCs), this material is also of interest for biological applications and fundamental physical studies. Until now, it was unclear how Ln:YLF NCs grow from their ionic precursors into tetragonal NCs with a well-defined, bipyramidal shape and uniform dopant distribution. Here, we study the nucleation and growth of ytterbium-doped LiYF4 (Yb:YLF), as a template for general Ln:YLF NC syntheses. We show that the formation of bipyramidal Yb:YLF NCs is a multistep process starting with the formation of amorphous Yb:YLF spheres. Over time, these spheres grow via Ostwald ripening and crystallize, resulting in bipyramidal Yb:YLF NCs. We further show that prolonged heating of the NCs results in the degradation of the NCs, observed by the presence of large LiF cubes and small, irregular Yb:YLF NCs. Due to the similarity in chemical nature of all lanthanide ions our work sheds light on the formation stages of Ln:YLF NCs in general.

Semen Analysis in "Urology-Naïve" Patients: A Chance of Uroandrological Screening in Young Males.

(1) Background: While females start their gynecological examinations during puberty, only few men decide to be visited by urologists in their youth. Given the participation in the EcoFoodFertility research project, our department had the opportunity to screen young males that were supposedly healthy. (2) Results: from January 2019 to July 2020, we evaluated 157 patients with sperm, blood analysis, and uroandrological examinations. The inclusion criteria were age 18-40 and absence of previous urological disease (urology-naïve). The primary endpoint of the study was to record uroandrological diseases that are occasionally discovered during examination in asymptomatic young men. The average age was 26.9 years (range 18-40); average testicular volume was 15.7 mL (range 12-22 mL); and 45.2% reported abnormal semen analysis: 62 cases of teratozoospermia, 27 asthenozoospermia, 18 oligozoospermia, and 2 azoospermia were discovered respectively; 4/157 patients were diagnosed with hypogonadism; 2 cases with suspicious testicular mass resulted in testicular cancer; and 31 suspected varicoceles and 8 patients with mild sexual dysfunctions were managed. (3) Conclusions: an uroandrological evaluation of young asymptomatic males allowed for the prompt diagnosis of different urological conditions, including cancerous ones, in our series. Despite being debatable, combining urological counselling with physical examination, semen analysis, and a laboratory profile could be useful and cost-effective in order to ameliorate male health.

Mixed Ligand Passivation as the Origin of Near-Unity Emission Quantum Yields in CsPbBr3 Nanocrystals.

Key features of syntheses, involving the quaternary ammonium passivation of CsPbBr3 nanocrystals (NCs), include stable, reproducible, and large (often near-unity) emission quantum yields (QYs). The archetypical example involves didodecyl dimethyl ammonium (DDDMA+)-passivated CsPbBr3 NCs where robust QYs stem from interactions between DDDMA+ and NC surfaces. Despite widespread adoption of this synthesis, specific ligand-NC surface interactions responsible for large DDDMA+-passivated NC QYs have not been fully established. Multidimensional nuclear magnetic resonance experiments now reveal a new DDDMA+-NC surface interaction, beyond established "tightly bound" DDDMA+ interactions, which strongly affects observed emission QYs. Depending upon the existence of this new DDDMA+ coordination, NC QYs vary broadly between 60 and 85%. More importantly, these measurements reveal surface passivation through unexpected didodecyl ammonium (DDA+) that works in concert with DDDMA+ to produce near-unity (i.e., >90%) QYs.

One-year outcomes after water vapor thermal therapy for symptomatic benign prostatic hyperplasia in an unselected Italian multicenter cohort.

BACKGROUND: Water vapor therapy (Rezum®; Boston Scientific, Marlborough, MA, USA) for bladder outflow obstruction (BOO) due to benign prostatic enlargement (BPE) is a minimally invasive and innovative surgical technique. The aim of this study was to evaluate its mid-term results in a large multicentric cohort of Italian patients. METHODS: Patients with BPO and moderate to severe LUTS who underwent Rezum® (Boston Scientific) treatment from May 2019 to July 2021 were included in this study. Pre- and postoperative evaluation comprised full urological evaluation with urine culture, digital rectal examination, serum PSA, transrectal prostate ultrasound, uroflowmetry, post-void residual and IPSS, OAB-q SF, ICIQ-UI SF and IIEF-5, ejaculatory anterograde rate. Minimum follow-up was 12 months. Patients' subjective satisfaction was recorded with Patient Global Impression of Improvement (PGI-I) Scale together with any early or late reported complications, classified according to Clavien-Dindo Scale. Statistical analysis was conducted as appropriate. RESULTS: Overall, 352 patients were eligible for the analysis. Procedures were routinely done on an outpatient basis. Mean operative was 12 minutes. The catheter was left in place for a median of 7 days. After treatment, Qmax, IPSS and IPSS-QoL, OAB-q SF, ICIQ-UI SF and IIEF-5 from baseline to last control follow-up (median 16, IQR 13-20 months) were improved (P<0.05). The postoperative anterograde ejaculation rate was recorded in 74.1% vs. preoperative 43.8% (P<0.001). Early (≤30 days) postoperative complications occurred in 176 patients (50%), all Clavien-Dindo Grade ≤2. One patient experienced clot retention and hematuria requiring hospitalization and blood transfusion. No late AEs were recorded. Surgical retreatment rate was 2.5% (9/352), all cases occurred within the first year. Median PGI-I was 2 (1-2). CONCLUSIONS: We confirmed the safety and efficacy of water vapor therapy for the treatment of symptomatic benign prostatic obstruction (BPO) on a large cohort of patients. Anterograde ejaculation was preserved in the majority of patients, with good subjective improvement. Further studies may rule out possible role of Rezum® (Boston Scientific) in new patients' setting.

Collective Diffraction Effects in Perovskite Nanocrystal Superlattices.

ConspectusFor almost a decade now, lead halide perovskite nanocrystals have been the subject of a steadily growing number of publications, most of them regarding CsPbBr3 nanocubes. Many of these works report X-ray diffraction patterns where the first Bragg peak has an unusual shape, as if it was composed of two or more overlapping peaks. However, these peaks are too narrow to stem from a nanoparticle, and the perovskite crystal structure does not account for their formation. What is the origin of such an unusual profile, and why has it been overlooked so far? Our attempts to answer these questions led us to revisit an intriguing collective diffraction phenomenon, known for multilayer epitaxial thin films but not reported for colloidal nanocrystals before. By analogy, we call it the multilayer diffraction effect.Multilayer diffraction can be observed when a diffraction experiment is performed on nanocrystals packed with a periodic arrangement. Owing to the periodicity of the packing, the X-rays scattered by each particle interfere with those diffracted by its neighbors, creating fringes of constructive interference. Since the interfering radiation comes from nanoparticles, fringes are visible only where the particles themselves produce a signal in their diffraction pattern: for nanocrystals, this means at their Bragg peaks. Being a collective interference phenomenon, multilayer diffraction is strongly affected by the degree of order in the nanocrystal aggregate. For it to be observed, the majority of nanocrystals within the sample must abide to the stacking periodicity with minimal misplacements, a condition that is typically satisfied in self-assembled nanocrystal superlattices or stacks of colloidal nanoplatelets.A qualitative understanding of multilayer diffraction might explain why the first Bragg peak of CsPbBr3 nanocubes sometimes appears split, but leaves many other questions unanswered. For example, why is the split observed only at the first Bragg peak but not at the second? Why is it observed routinely in a variety of CsPbBr3 nanocrystals samples and not just in highly ordered superlattices? How does the morphology of particles (i.e., nanocrystals vs nanoplatelets) affect the appearance of multilayer diffraction effects? Finally, why is multilayer diffraction not observed in other popular nanocrystals such as Au and CdSe, despite the extensive investigations of their superlattices?Answering these questions requires a deeper understanding of multilayer diffraction. In what follows, we summarize our progress in rationalizing the origin of this phenomenon, at first through empirical observation and then by adapting the diffraction theory developed in the past for multilayer thin films, until we achieved a quantitative fitting of experimental diffraction patterns over extended angular ranges. By introducing the reader to the key advancements in our research, we provide answers to the questions above, we discuss what information can be extracted from patterns exhibiting collective interference effects, and we show how multilayer diffraction can provide insights into colloidal nanomaterials where other techniques struggle. Finally, with the help of literature patterns showing multilayer diffraction and simulations performed by us, we demonstrate that this collective diffraction effect is within reach for many appealing nanomaterials other than halide perovskites.

Are Mixed-Halide Ruddlesden-Popper Perovskites Really Mixed?

Mixing bromine and iodine within lead halide perovskites is a common strategy to tune their optical properties. This comes at the cost of instability, as illumination induces halide segregation and degrades device performances. Hence, understanding the behavior of mixed-halide perovskites is crucial for applications. In 3D perovskites such as MAPb(Br x I1-x )3 (MA = methylammonium), all of the halide crystallographic sites are similar, and the consensus is that bromine and iodine are homogeneously distributed prior to illumination. By analogy, it is often assumed that Ruddlesden-Popper layered perovskites such as (BA)2MAPb2(Br x I1-x )7 (BA = butylammonium) behave alike. However, these materials possess a much wider variety of halide sites featuring diverse coordination environments, which might be preferentially occupied by either bromine or iodine. This leaves an open question: are mixed-halide Ruddlesden-Popper perovskites really mixed? By combining powder and single-crystal diffraction experiments, we demonstrate that this is not the case: bromine and iodine in RP perovskites preferentially occupy different sites, regardless of the crystallization speed.

Cu+ → Mn2+ Energy Transfer in Cu, Mn Coalloyed Cs3ZnCl5 Colloidal Nanocrystals.

In this work, we report the hot-injection synthesis of Cs3ZnCl5 colloidal nanocrystals (NCs) with tunable amounts of Cu+ and Mn2+ 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 Cs3ZnCl5 NCs, and Cu ions were mainly introduced in the oxidation state +1 according to X-ray photoelectron and electron paramagnetic resonance spectroscopies. The spectroscopic analysis of unalloyed, Cu-alloyed, Mn-alloyed, and Cu, Mn coalloyed NCs indicated that (i) the Cs3ZnCl5 NCs have a large band gap of ∼5.35 eV; (ii) Cu(I) aliovalent alloying leads to an absorption shoulder/peak at ∼4.8 eV and cyan photoluminescence (PL) peaked at 2.50 eV; (iii) Mn(II) isovalent alloying leads to weak Mn PL, which intensifies remarkably in the coalloyed samples, prompted by an energy transfer (ET) process between the Cu and Mn centers, favored by the overlap between the lowest (6A1 → 4T1) transition for tetrahedrally coordinated Mn2+ and the PL profile from Cu(I) species in the Cs3ZnCl5 NCs. The efficiency of this ET process reaches a value of 61% for the sample with the highest extent of Mn alloying. The PL quantum yield (QY) values in these Cu, Mn coalloyed NCs are lower at higher Mn contents. The analysis of the Mn PL dynamics in these samples indicates that this PL drop stems from inter-Mn exciton migration, which increases the likelihood of trapping in defect sites, in agreement with previous studies.

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. Inspired by such approach, we demonstrate the use of CsPbCl3 perovskite nanocrystals to drive the phase-selective synthesis of two yet unexplored lead sulfochlorides: Pb3S2Cl2 and Pb4S3Cl2. When homogeneously nucleated in solution, lead sulfochlorides form Pb3S2Cl2 nanocrystals. Conversely, the presence of CsPbCl3 triggers the formation of Pb4S3Cl2/CsPbCl3 epitaxial heterostructures. The phase selectivity is guaranteed by the continuity of the cationic subnetwork across the interface, a condition not met in a hypothetical Pb3S2Cl2/CsPbCl3 heterostructure. The perovskite domain is then etched, delivering phase-pure Pb4S3Cl2 nanocrystals that could not be synthesized directly.

Colloidal Bismuth Chalcohalide Nanocrystals.

Here we present a colloidal approach to synthesize bismuth chalcohalide nanocrystals (BiEX NCs, in which E=S, Se and X=Cl, Br, I). Our method yields orthorhombic elongated BiEX NCs, with BiSCl crystallizing in a previously unknown polymorph. The BiEX NCs display a composition-dependent band gap spanning the visible spectral range and absorption coefficients exceeding 105  cm-1 . The BiEX NCs show chemical stability at standard laboratory conditions and form colloidal inks in different solvents. These features enable the solution processing of the NCs into robust solid films yielding stable photoelectrochemical current densities under solar-simulated irradiation. Overall, our versatile synthetic protocol may prove valuable in accessing colloidal metal chalcohalide nanomaterials at large and contributes to establish metal chalcohalides as a promising complement to metal chalcogenides and halides for applied nanotechnology.

Red-emissive nanocrystals of Cs4MnxCd1-xSb2Cl12 layered perovskites.

Layered double perovskites are currently being investigated as emerging halide-based materials for optoelectronic applications. Herein, we present the synthesis of Cs4MnxCd1-xSb2Cl12 (0 ≤ x ≤ 1) nanocrystals (NCs). X-ray powder diffraction evidences the retention of the same crystal structure for all the inspected compositions; transmission electron microscopy revealed monodisperse particles with a mean size between 10.7 nm and 12.7 nm. The absorption spectra are mostly determined by transitions related to Sb3+, whereas Mn2+ induced a red emission in the 625-650 nm range. The photoluminescence emission intensity and position vary with the Mn2+ content and reach the maximum for the composition with x = 0.12. Finally, we demonstrate that the photoluminescence quantum yield of the latter NCs was increased from 0.3% to 3.9% through a post-synthesis treatment with ammonium thiocyanate. The present work expands the knowledge of colloidal layered double perovskite nanocrystals, stimulating future investigations of this emerging class of materials.

Psychological distress among patients awaiting histopathologic results after prostate biopsy: An unaddressed concern.

BACKGROUND: Prostate cancer is the most commonly diagnosed neoplasm in men. From the introduction of PSA testing, an increasing number of men undergoes prostate biopsy (PBX). While the physical side effects of PBx have been well investigated, its psychological impact has been under-evaluated. AIM: The aim of our study is to investigate the presence of psychological distress (anxiety and depression) in patients waiting for histopathological results after prostate biopsy (PBx). METHODS: From February to April 2019, 51 consecutive patients undergoing prostate biopsies at our institution were included. Age, PSA, DRE, familiarity for prostate cancer, number of previous biopsies, type of anesthesia, number of cores were recorded. All patients filled the Hospital Anxiety and Depression Scale (HADS), a psychometric Likert-scale questionnaire, before receiving the histopathological results of their PBx. RESULTS: The prevalence of psychological distress among patients awaiting histopathologic results is 41% (21/51 patients), with anxiety being the main component of their distress. On multivariate analysis, PSA, family history, and repeat biopsy were significantly associated with anxiety and depression. CONCLUSION: Patients undergoing PBx experience a burden of psychological distress waiting for histopathologic results, especially anxiety. Appropriate counseling should be offered to patients at high risk of developing psychological distress after PBx. Future goals would include technological improvements to shorten the time between biopsy and definitive results.

Structure and Surface Passivation of Ultrathin Cesium Lead Halide Nanoplatelets Revealed by Multilayer Diffraction.

The research on two-dimensional colloidal semiconductors has received a boost from the emergence of ultrathin lead halide perovskite nanoplatelets. While the optical properties of these materials have been widely investigated, their accurate structural and compositional characterization is still challenging. Here, we exploited the natural tendency of the platelets to stack into highly ordered films, which can be treated as single crystals made of alternating layers of organic ligands and inorganic nanoplatelets, to investigate their structure by multilayer diffraction. Using X-ray diffraction alone, this method allowed us to reveal the structure of ∼12 Šthick Cs-Pb-Br perovskite and ∼25 Šthick Cs-Pb-I-Cl Ruddlesden-Popper nanoplatelets by precisely measuring their thickness, stoichiometry, surface passivation type and coverage, as well as deviations from the crystal structures of the corresponding bulk materials. It is noteworthy that a single, readily available experimental technique, coupled with proper modeling, provides access to such detailed structural and compositional information.

Halide Perovskite-Lead Chalcohalide Nanocrystal Heterostructures.

We report the synthesis of colloidal CsPbX3-Pb4S3Br2 (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 CsPbBr3-Pb4S3Br2 nanocrystals are prepared by a two-step direct synthesis using preformed subnanometer CsPbBr3 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. Postsynthesis reaction with either Cl- or I- ions delivers the corresponding CsPbCl3-Pb4S3Br2 and CsPbI3-Pb4S3Br2 heterostructures, thus enabling anion exchange only in the perovskite domain. An increased structural rigidity is conferred to the perovskite lattice when it is interfaced with the chalcohalide lattice. This is attested by the improved stability of the metastable γ phase (or "black" phase) of CsPbI3 in the CsPbI3-Pb4S3Br2 heterostructure.

Metamorphoses of Cesium Lead Halide Nanocrystals.

Following the impressive development of bulk lead-based perovskite photovoltaics, the "perovskite fever" did not spare nanochemistry. In just a few years, colloidal cesium lead halide perovskite nanocrystals have conquered researchers worldwide with their easy synthesis and color-pure photoluminescence. These nanomaterials promise cheap solution-processed lasers, scintillators, and light-emitting diodes of record brightness and efficiency. However, that promise is threatened by poor stability and unwanted reactivity issues, throwing down the gauntlet to chemists.More generally, Cs-Pb-X nanocrystals have opened an exciting chapter in the chemistry of colloidal nanocrystals, because their ionic nature and broad diversity have challenged many paradigms established by nanocrystals of long-studied metal chalcogenides, pnictides, and oxides. The chemistry of colloidal Cs-Pb-X nanocrystals is synonymous with change: these materials demonstrate an intricate pattern of shapes and compositions and readily transform under physical stimuli or the action of chemical agents. In this Account, we walk through four types of Cs-Pb-X nanocrystal metamorphoses: change of structure, color, shape, and surface. These transformations are often interconnected; for example, a change in shape may also entail a change of color.The ionic bonding, high anion mobility due to vacancies, and preservation of cationic substructure in the Cs-Pb-X compounds enable fast anion exchange reactions, allowing the precise control of the halide composition of nanocrystals of perovskites and related compounds (e.g., CsPbCl3 ⇄ CsPbBr3 ⇄ CsPbI3 and Cs4PbCl6 ⇄ Cs4PbBr6 ⇄ Cs4PbI6) and tuning of their absorption edge and bright photoluminescence across the visible spectrum. Ion exchanges, however, are just one aspect of a richer chemistry.Cs-Pb-X nanocrystals are able to capture or release (in short, trade) ions or even neutral species from or to the surrounding environment, causing major changes to their structure and properties. The trade of neutral PbX2 units allows Cs-Pb-X nanocrystals to cross the boundaries among four different types of compounds: 4CsX + PbX2 ⇄ Cs4PbBr6 + 3PbX2 ⇄ 4CsPbBr3 + PbX2 ⇄ 4CsPb2X5. These reactions do not occur at random, because the reactant and product nanocrystals are connected by the Cs+ cation substructure preservation principle, stating that ion trade reactions can transform one compound into another by means of distorting, expanding, or contracting their shared Cs+ cation substructure.The nanocrystal surface is a boundary between the core and the surrounding environment of Cs-Pb-X nanocrystals. The surface influences nanocrystal stability, optical properties, and shape. For these reasons, the dynamic surface of Cs-Pb-X nanocrystals has been studied in detail, especially in CsPbX3 perovskites. Two takeaways have emerged from these studies. First, the competition between primary alkylammonium and cesium cations for the surface sites during the CsPbX3 nanocrystal nucleation and growth governs the cube/plate shape equilibrium. Short-chain acids and branched amines influence that equilibrium and enable shape-shifting synthesis of pure CsPbX3 cubes, nanoplatelets, nanosheets, or nanowires. Second, quaternary ammonium halides are emerging as superior ligands that extend the shelf life of Cs-Pb-X colloidal nanomaterials, boost their photoluminescence quantum yield, and prevent foreign ions from escaping the nanocrystals. That is accomplished by combining reduced ligand solubility, due to the branched organic ammonium cation, with the surface-healing capabilities of the halide counterions, which are small Lewis bases.

Multilayer Diffraction Reveals That Colloidal Superlattices Approach the Structural Perfection of Single Crystals.

Colloidal superlattices are fascinating materials made of ordered nanocrystals, yet they are rarely called "atomically precise". That is unsurprising, given how challenging it is to quantify the degree of structural order in these materials. However, once that order crosses a certain threshold, the constructive interference of X-rays diffracted by the nanocrystals dominates the diffraction pattern, offering a wealth of structural information. By treating nanocrystals as scattering sources forming a self-probing interferometer, we developed a multilayer diffraction method that enabled the accurate determination of the nanocrystal size, interparticle spacing, and their fluctuations for samples of self-assembled CsPbBr3 and PbS nanomaterials. The multilayer diffraction method requires only a laboratory-grade diffractometer and an open-source fitting algorithm for data analysis. The average nanocrystal displacement of 0.33 to 1.43 Å in the studied superlattices provides a figure of merit for their structural perfection and approaches the atomic displacement parameters found in traditional crystals.