Nanocrystals Research Articles

High‐Resolution X‐Ray Imaging With 0D Organic–Metal Halide Scintillator Featuring Reversed Exciton Trapping

AbstractScintillators, essential for applications in nuclear medicine, radiation detection, and industrial inspection, convert high‐energy radiation into visible light. Manganese (Mn)‐based inorganic–organic hybrid materials are distinguished by their thermal stability, mechanical strength, and flexibility. However, the effects of temperature on Mn(II)‐based hybrid scintillators have not been clearly analyzed, making the elucidation of their temperature‐dependent luminescence mechanisms particularly important. A notable advancement is the synthesis of Mn‐1 nanocrystals (NCs) using methyltriphenylphosphonium chloride (mtppCl) and MnCl₂. These NCs exhibit distinctive temperature‐dependent photoluminescence luminescence: the intensity decreases from 77 to 150 K but paradoxically increases at higher temperatures due to anomalous thermal exciton behavior in the [MnCl₄]2⁻ tetrahedra. Besides, Mn‐1 NCs achieve a detection limit of 1.01 µGyair/s, surpassing medical diagnostic standards and outperforming commercial scintillators such as Bi₄Ge₃O₁₂ (BGO). Additionally, they show exceptional stability under continuous irradiation and can be incorporated into a flexible scintillating film with a resolution of 11.3 lp/mm at an MTF of 0.2. The current study has further refined the luminescence mechanism of Mn(II)‐based materials and optimizes their properties for a wider range of applications.

Micrometer-Resolution Fluorescence and Lifetime Mappings of CsPbBr3 Nanocrystal Films Coupled with a TiO2 Grating.

Enhancing light emission from perovskite nanocrystal (NC) films is essential in light-emitting devices, as their conventional stacks often restrict the escape of emitted light. This work addresses this challenge by employing a TiO2 grating to enhance light extraction and shape the emission of CsPbBr3 nanocrystal films. Angle-resolved photoluminescence (PL) demonstrated a 10-fold increase in emission intensity by coupling the Bloch resonances of the grating with the spontaneous emission of the perovskite NCs. Fluorescence lifetime imaging microscopy (FLIM) provided micrometer-resolution mapping of both PL intensity and lifetime across a large area, revealing a decrease in PL lifetime from 8.2 ns for NC films on glass to 6.1 ns on the TiO2 grating. Back focal plane (BFP) spectroscopy confirmed how the Bloch resonances transformed the unpolarized, spatially incoherent emission of NCs into polarized and directed light. These findings provide further insights into the interactions between dielectric nanostructures and perovskite NC films, offering possible pathways for designing better performing perovskite optoelectronic devices.

Light-induced synthesis of Highly stable CsPbCl3:Mn2+@mSiO2 nanocomposites for white Light-Emitting Diodes

All-inorganic perovskite nanocrystals (NCs) exhibit great promise in optoelectronics and photovoltaics. However, their intrinsic low-thermal/oxygen/moisture stability and the rigorous synthesis procedures have limited the practical applications. Here, we present a facile, one-step, light-induced method to synthesize CsPbCl3:Mn2+ NCs at room temperature by using carbon tetrachloride (CCl4) as the halide source. The corresponding formation mechanism of CsPbCl3:Mn2+ NCs is revealed, where CsPbCl3:Mn2+ NCs are formed through the direct incorporation of [MnCl6]4− octahedral into the perovskite lattice during the nucleation and growth process. Additionally, we demonstrate the in-situ growth of CsPbCl3:Mn2+ NCs within mesoporous silica (mSiO2) spheres to form CsPbCl3:Mn2+@mSiO2 nanocomposites via the light-induced method, resulting in a remarkable improvement in high-temperature and long-time stability. As a prototype experiment, a white light-emitting diode (WLED) device is constructed using CsPbCl3:Mn2+@mSiO2 nanocomposites, which exhibits a bright white-light emission with the CIE chromaticity coordinate of (0.352, 0.340). It is anticipated that light-induced synthesis method provides a straightforward strategy for synthesizing multifunctional halide perovskite nanocrystals and nanocomposites for versatile applications.

Formononetin-Loaded Self-Microemulsion Drug Delivery Systems for Improved Solubility and Oral Bioavailability: Fabrication, Characterization, In Vitro and In Vivo Evaluation.

This study aimed to construct a self-microemulsion drug delivery system (SMEDDS) for Formononetin (FMN) to improve its solubility and bioavailability while combining the nanocrystals (NCs) technology. The SMEDDS prescription composition was optimized with a pseudo-three-phase diagram, followed by a series of in vitro and in vivo evaluations of the selected optimal prescriptions. FMN-NCs loaded SMEDDS showed a homogeneous spherical shape in the Transmission electron microscope and the particle size was measured as (20.65 ± 1.42) nm. The in vitro cumulative release rate in each dissolution medium within 30min was higher than 80%, much higher than that of FMN (6%) and FMN-NCs (40%); Cellular experiments confirm that the formulation has a high safety profile and significantly promotes cellular uptake. The results of pharmacokinetics and intestinal absorption in rats showed that the relative bioavailability of FMN-NCs and FMN-NCs loaded SMEDDS were (154.80 ± 3.76)% and (557.73 ± 32.88)%, respectively, and both of them significantly increased the rate and extent of absorption of the drug in intestinal segments. FMN-NCs loaded SMEDDS significantly enhanced the solubility and bioavailability of FMN.

Triple-Mode Protection with Ln3+ Ion-Doped Core-Heptad-Shell Single Nanocrystals for High-Level Security Applications.

In this work, oleic acid (OA)-capped core-heptad-shell (CHS) nanocrystals (NCs) that exhibit multiple emissions achieved through downshifting and orthogonal upconversion are synthesized via layer-by-layer thermal decomposition. This method enables the downshifting process to be accommodated by doping ions in the inert space between two upconversion patterns (the core and fourth shell) and doping Ce/Tb or Ce/Eu ions in the NaGdF4 layer for the first time. These developed CHS NCs exhibit different emission colors via 980 and 800 nm orthogonal upconversion and downshifting emissions under 256 nm UV excitation in hexane solvent. Furthermore, surface-functionalized OA is removed using mild acid treatment. The resulting bare CHS NCs disperse well in water and exhibit 21.60-fold and 43.59-fold higher Ce/Tb and Ce/Eu luminescence intensities, respectively, than the OA-capped CHS NCs. These NCs are mixed with a carboxymethylcellulose (CMC) polymer in an aqueous medium to form a CMC-CHS NC gel. Invisible patterns and QR codes are printed on nonfluorescent paper using gels and screen-printing techniques. These patterns and QR codes exhibit three different emission colors under three different excitations. This method can be used for high-level anticounterfeiting applications.

Anion regulation for surface passivation enables ultrahigh-stability perovskite nanocrystals.

All-inorganic perovskite CsPbBr3 nanocrystals (NCs) display high photoluminescence quantum yield and narrow emission, which show great potential application in optoelectronic devices. However, the poor environment stability of NCs will hinder their practical application. Herein, a series of ionic liquids with different anions (BF4-, Br-, and NO3-) were used as a sole capping ligand to synthesize NCs. Among the three samples, 1-hexadecyl-3-methylimidazolium tetrafluoroborate ([C16MIM]BF4) capped NCs have the highest stability in light, thermal, and water, possibly attributing to the in situ passivation of bromine vacancy via pseudohalogen BF4- and tight binding of ionic liquid ligands and lead atoms. In addition, green-emission [C16MIM]BF4 NCs were used to assemble a white light-emitting diode device, and it possessed a wide National Television System Committee color gamut of 124.5% and a stable emission peak at high driving currents of 380 mA. This work paves the way for resurfacing perovskite NCs with ultrahigh stability, thereby driving the perovskite NC display industry closer to real-world application.

Kirkendall Effect-Driven Reversible Chemical Transformation for Reconfigurable Nanocrystals.

The potential universality of chemical transformation principles makes it a powerful tool for nanocrystal (NC) synthesis. An example is the nanoscale Kirkendall effect, which serves as a guideline for the construction of hollow structures with different properties compared to their solid counterparts. However, even this general process is still limited in material scope, structural complexity, and, in particular, transformations beyond the conventional solid-to-hollow process. We demonstrate in this work an extension of the Kirkendall effect that drives reversible structural and phase transformations between metastable metal chalcogenides (MCs) and metal phosphides (MPs). Starting from Ni3S4/Cu1.94S NCs as the initial frameworks, ligand-regulated sequential extractions and diffusion of host/guest (S2-/P3-) anions between Ni3S4/Cu1.94S and Ni2P/Cu3P phases enable solid-to-hollow-to-solid structural motif evolution while retaining the overall morphology of the NC. An in-depth mechanistic study reveals that the transformation between metastable MCs and MPs occurs through a combination of ligand-dependent kinetic control and anion mixing-induced thermodynamic control. This strategy provides a robust platform for creating a library of reconfigurable NCs with tunable compositions, structures, and interfaces.

Colloidal Synthesis of Blue-Emitting Cs3TmCl6 Nanocrystals via Localized Excitonic Recombination for Down-Conversion White Light-Emitting Diodes.

Lead-halide perovskite nanocrystals (NCs) have gained significant attention for their promising applications in lighting and display technologies. However, blue-emitting NCs have struggled to match the high efficiency of their red and green counterparts. Moreover, many reported blue-emitting perovskite NCs contain heavy metal lead (Pb), which poses risks to human health and the environment. In this study, we synthesized rare-earth-based Cs3TmCl6 NCs via the hot injection method, which exhibit a broadband blue emission at 440 nm. Combined experimental and theoretical studies indicate that the broadband emission in Cs3TmCl6 arises from self-trapped excitons due to the excited-state structural distortion of the [TmCl6]3- cluster. Furthermore, the ultrafast dynamics of charge carriers were analyzed using time-resolved photoluminescence and transient absorption measurements. Encouraged by the remarkable thermal, light, and water stabilities of Cs3TmCl6 NCs, as evidenced by experimental and theoretical results, a white light-emitting diode was further designed and fabricated using the Cs3TmCl6 NCs as the color converter. The device exhibits outstanding performance, achieving a long half-lifetime of 336 h and a large color-rendering index of 87.0. Combining eco-friendly features and a facile synthesis method, the rare-earth-based Cs3TmCl6 NCs mark a significant breakthrough as a reliable blue emitter, showcasing their future potential in lighting and display applications.

Ambient Air-Synthesized CsPbBr3 Nanocrystals Coupled with TiO2 Film as an Efficient Hybrid Photoanode for Photoelectrochemical Methanol-to-Formaldehyde Conversion.

Due to its exceptional optoelectronic properties in the visible spectrum, cesium lead bromide (CsPbBr3) perovskite has attracted considerable attention in solar-driven organic transformations via photoelectrochemical (PEC) cells. However, the performance of the devices is adversely affected by electron-hole recombination occurring between a transparent conductive substrate, such as fluorine-doped tin dioxide (FTO), and a perovskite layer. Herein, to mitigate this issue, a compact layer of titanium dioxide (TiO2) was employed as both an electron transport layer and a hole blocking layer to diminish charge recombination while facilitating electron transfer in such perovskite material. At the oxidation peak potential of 0.70 V vs Ag/AgNO3, a hybrid photoanode of CsPbBr3/TiO2/FTO exhibited a significant increase in photocurrent density, from 15 to 41 μA/cm2, compared to a configuration without a TiO2 layer. Furthermore, the introduction of methanol as a hole scavenger in the PEC system using the hybrid photoanode facilitated the separation of electron-hole pairs, which led to an enhanced photocurrent density of 60 μA/cm2 and promoted the production of formaldehyde. High-performance liquid chromatography (HPLC) confirmed the generation of formaldehyde at a concentration of 26.69 μM with a Faradaic efficiency of 92% under an applied potential of 0.50 V vs Ag/AgNO3 for 60 min of PEC reaction. In addition to the enhanced PEC performance achieved from this hybrid photoanode, CsPbBr3 nanocrystals (NCs) in this work were synthesized by the modified one-pot method under ambient air, where highly uniform and high-purity NCs were obtained. This work signifies the groundbreaking exploration of CsPbBr3 NCs with TiO2 as a photoelectrode material in the organic-based PEC cells, which efficiently improved the interfacial charge transfer within the photoanode for the conversion of methanol to formaldehyde, marking a significant advancement in the field.

Solvent-Free in Situ Synthesis of a CsPbBr3 Nanocrystal/ZrO2 Hybrid Phosphor with Excellent Thermal Stability for White Light-Emitting Diodes.

All-inorganic cesium lead halide perovskite CsPbX3 (X = Cl, Br, I, or mixed) nanocrystals (NCs) are emerging as promising candidates in light-emitting diodes (LEDs) owing to their excellent luminescent properties. However, CsPbX3 NCs are extremely susceptible to the elevated temperature associated with prolonged LED operation due to their low formation energy and soft ionic crystal structure. Here, CsPbBr3 NCs hybridized with ZrO2 were in situ synthesized by a rapid solvent-free method under an ambient environment for the first time, which was also suitable for large-scale production. The as-prepared CsPbBr3/ZrO2 hybrid phosphor not only presented enhanced photoluminescence (PL) properties but also exhibited improved thermal stability. For example, the PL intensity of the CsPbBr3/ZrO2 hybrid phosphor could retain 70% of the initial value at 130 °C, obviously higher than that of 34% for pure CsPbBr3. The exceptional thermal stability of the CsPbBr3/ZrO2 hybrid phosphor could be attributed to the introduction of ZrO2, which effectively preserved the initial perovskite structure of CsPbBr3 during heat treatment, as confirmed by XRD results. The as-prepared CsPbBr3/ZrO2 hybrid phosphor had great practical applications verified by the construction of white LEDs (WLEDs) with a luminance degradation of only 9% after continuous operation for 24 h at the initial luminance of 2000 cd m-2, which was significantly better than that of 63% for control WLEDs. The proposed thermally stable hybrid phosphor is expected to greatly contribute to the industrialization process of perovskites.

Single-Nanometer Spinel with Precise Cation Distribution for Enhanced Oxygen Reduction.

Designing spinel nanocrystals (NCs) with tailored structural composition and cation distribution is crucial for superior catalytic performance but remarkably challenging due to their intricate nature. Here, an aggregation growth restricted hot-injection method is presented by meticulously investigating the fundamental nucleation and aggregation-driven growth kinetics governing spinel NC formation to address this challenge. Through controlled collision probability of nuclei during growth, this approach enables the synthesis of spinel NCs with unprecedented, single nanometer (1.2nm). Single-nanometer CoMn2O4 spinel via this method exhibits a highly tailored structure with a maximized population of highly active octahedral Mn atoms, thereby optimizing oxygen intermediate adsorption during oxygen reduction reaction (ORR). Consequently, it exhibits a remarkable half-wave potential of 0.88V in ORR and leads to a superior power density (170.9mW cm-2) in zinc-air battery, outperforming commercial Pt/C and most reported spinel oxides, revealing a clear structure-property relationship. This structure design strategy is readily adaptable for the precise synthesis and engineering of various spinel structures, opening new avenues for developing advanced electrocatalysts and energy storage materials.

Dual-shell protection enables highly efficient and stable all-inorganic perovskite composites for light-emitting-diodes

Lead-halide perovskite nanocrystals (NCs) present superior photoelectric properties, but the poor stability seriously hinders their practical application. The encapsulation of perovskite NCs inside mesoporous silica (m-SiO2) matrix is considered as one of the most feasible pathways to improve the stability of NCs. However, the challenges of loose encapsulation structure, aggregation of particles, high energy consumption during the preparation of CsPbX3@m-SiO2 composites have not yet been overcome, which throw a shadow over the large-scale commercial applications. Here, we present a dual-shell encapsulation strategy that enables the formation of highly emissive CsPbBr3@m-SiO2@SiO2 composites, achieving an exceptional photoluminescence quantum yield (PLQY) of 97.37 %. The reaction parameters for the preparation of composites are meticulous investigated. The CsPbBr3 NCs can be well formed inside the pores of m-SiO2 as the m-SiO2 is introduced into the precursor solution. The secondary SiO2 shells can effectively seal the open pores of m-SiO2. As a result, the as-prepared CsPbBr3@m-SiO2@SiO2 composites present excellent stability, in which the composites can maintain 93.16 % of initial intensity after storage for 84 days. Besides, a series of CsPbX3@m-SiO2@SiO2 composites with tunable emission wavelength in the range of 428.6–630.6 nm are prepared through facile designing the halide ratios of precursor solution, which present a wide color gamut (148.48 % of the National Television Standards Committee). In addition, a white light-emitting diode (LED) is fabricated by combining CsPbBr3@m-SiO2@SiO2 composites and K2SiF6:Mn4+ phosphors with a 455 nm LED chip, which exhibits good photoelectric performances. This facile low-temperature dual-shell encapsulation strategy reported here provides a new pathway for preparing high-performance perovskite composites, facilitating their practical photoelectric application.

Sodium Assists Controlled Synthesis of Cubic Rare-Earth Oxyfluorides Nanocrystals for Information Encryption and Near-Infrared-IIb Bioimaging.

Rare-earth oxyfluoride (REOF) colloidal nanocrystals (NCs) suffer from a low photoluminescence efficiency due to their small size with poor crystallinity and a detrimental surface quenching effect. Herein, we introduce an innovative approach that involves doping sodium ions into REOF NCs to produce monodisperse, size-controllable, well-crystallized, and highly luminescent colloidal REOF core/shell NCs. The Na+ doping allows for successfully synthesizing the cubic REOF NCs with a tunable size from 6 to 30 nm. Further fabrication of the core/shell NCs doped with Na+ results in enhancements up to 1062 (Ho3+), 1140 (Er3+), and 2212 (Tm3+) folds in upconversion luminescence and 17.7 folds (Er3+) in downconversion luminescence compared to that of core/shell NCs without doping Na+ ions. These NCs were subsequently developed into multicolor luminescent inks, demonstrating significant potential application for information security, and used for near-infrared-IIb (NIR-IIb) (1500-1700 nm) in vivo imaging, which exhibits a high-resolution in vivo dynamic imaging capability with a signal-to-noise ratio of 5.28. These results present the way to the controlled synthesis of efficient luminescent cubic LuOF: RE3+/LuOF core/shell NCs, expanding the toolkit of rare-earth doped NCs in diverse applications such as advanced encoding encryption, varied fluorescence imaging, and biomedicine.

Selective Detection of Chromate and Permanganate Ions Using Gallic Acid Capped CaF2:Tb3+ Nanocrystals.

In this study, we have developed ligand-sensitized Ln3+-doped nanocrystals (NCs) for the selective sensing of Cr2O7 2- and MnO4 - ions in nanomolar concentrations. This is accomplished with the gallic acid capped-CaF2:Tb3+ NCs. These NCs display bright green emission through an efficient energy transfer from surface functionalized gallic acid molecules to Tb3+ ions upon UV light excitation. The luminescence from Tb3+ ions are selectively quenched by the addition of Cr2O7 2- and MnO4 - anions. The reduction in the luminescence intensity is found to be quite selective, as the addition of other strong oxidizing species (I-, F-, Br-, Cl-, PO3 2-, SO4 2-, VO3 -, WO4 2-, IO3 -, ClO4 -,) had minimal impact on the luminescence intensity of Tb3+ ions. The calculated limit of detection from the experimental results (for the 3σ/slope criterion) is 77 nM and 55 nM for K2Cr2O7 and KMnO4, respectively. The findings show that tuning the resonance energy transfer (RET) between analytes and Tb3+ inside the NCs serves as a tool for the detection of dichromate and permanganate ions selectively.

CsPbX3 Nanocrystal Incorporating Transition Metal Cocatalyst for Photocatalytic Organic Transformation by Single Electron Transfer

ABSTRACTThe construction of composite photocatalysts is a promising strategy for improving the overall catalytic efficiency in organic photochemical transformation. In this study, we synthesize a series of inorganic metal perovskite CsPbX3 (X = Cl, Br, I) nanocrystals (NCs) with excellent chemical stability and wide‐range visible‐light absorption. The Pd cocatalyst is then induced to the surfaces of CsPbX3 fabricating Pd/CsPbX3 composites via visible‐light reduction method. Photoelectrochemical measurements show the introduction of Pd cocatalyst promotes efficiently the charge separation and transfer of CsPbX3. The prepared Pd/CsPbX3 composites exhibit remarkable photocatalytic efficiency in visible‐light‐induced C–C cross‐coupling reaction. The reaction is characterized by mild reaction conditions, good recyclability, and high yield from a broad variety of substrates. Mechanism investigations show the reaction relies on the synergy of CsPbX3 photocatalysis and Pd catalysis. The valence band of CsPbX3 oxidizes the phenylboronic acid into active radical species via single electron transfer. On another hand, Pd(0) as active sites occurs oxidative addition with aryl halides for achieving the C–C cross‐coupling reaction. This study displays a feasible approach for the introduction of Pd catalyst in CsPbX3 to achieve the photocatalytic organic transformation via photoinduced electron transfer.

Intranasal nanocrystals of tadalafil: in vitro characterisation and in vivo pharmacokinetic study

Tadalafil (TDA) is a class II drug of the biopharmaceuticals classification system (BCS), with limited aqueous solubility and high permeability. This study aims to improve the bioavailability of poorly soluble tadalafil by developing intranasal nanocrystals (NCs) of TDA. TDANCs that were stabilised by polyvinyl alcohol (PVA) had the lowest size and the best solubility. F11 had a 196 nm in size with PDI and zeta potential of 0.21 and -11.20, respectively, which shows 5.5 and 1.6-fold higher in solubility (9.37 ± 0.36 μg/mL) and dissolution (50.11 ± 1.69%) than pure tadalafil, respectively. An in vivo animal study demonstrated that the maximum plasma concentration (Cmax) and total area under the curve (AUC0∞) achieved in the TDANCs group were 352.77 ± 35.17 ng/mL and 3377 ± 558 ng.h/mL, respectively, and were significantly higher than the pure TDA group after intranasal administration. In conclusion, TDANCs were successfully prepared by the sonoprecipitation technique, with significant enhancement in in vitro and in vivo properties. Therefore, intranasal administration of TDA nanocrystals was a good model for the treatment of erectile dysfunction.

Deciphering Surface Ligand Density of Colloidal Semiconductor Nanocrystals: Shape Matters.

Surface chemistry of colloidal semiconductor nanocrystals (NCs) is of paramount importance because it profoundly impacts their physical and chemical properties, processing, and performance. Herein, we report the effect of the shape of ZnS NCs in terms of nanodots, nanorods, and nanoplatelets (NPL) on the surface ligand density (LD) of the commonly used oleylamine (OLA) ligand by combining three experimental quantification techniques (e.g., thermogravimetric analysis-differential scanning calorimetry, 1H nuclear magnetic resonance spectroscopy, and inductively coupled plasma-optical emission spectrometry) with the semiempirical molecular dynamics (MD) simulations. Consistent results on the surface LD derived by the aforementioned three independent techniques were obtained, presenting an ascending order of LDdots < LDrods < LDNPLs. MD simulations reveal that the highest LD for ZnS NPLs can be attributed to their extremely flat and uniform surfaces with regular distribution of surface Zn atoms for the OLA molecules to achieve parallel and tight stacking, while for ZnS nanodots and nanorods, their surfaces may have staggered arrangement and multisteps, making it unlikely for the OLA ligand to adopt the tight ligand stacking mode. The finding revealed in this work not only sheds light on the constitution of the molecule ligand shell of NCs, which is helpful for their rational morphology control, but also provides an additional and important knob for tuning their chemical functionality.

Intense Circular Dichroism and Spin Selectivity in AgBiS2 Nanocrystals by Chiral Ligand Exchange.

Chiral semiconducting nanomaterials offer many potential applications in photodetection, light emission, quantum information, and so on. However, it is difficult to achieve a strong circular dichroism (CD) signal in semiconducting nanocrystals (NCs) due to the complexity of chiral ligand surface engineering and multiple, uncertain mechanisms of chiroptical behavior. Here, a chiral ligand exchange strategy with cysteine on the ternary metal chalcogenide AgBiS2 NCs is developed, and a strong, long-lasting CD signal in the near-UV region is achieved. By carefully optimizing the ligand concentration, the CD peaks are observed at 260 and 320nm, respectively, giving insight into the different ligand binding mechanisms influencing the CD signal of AgBiS2 NCs. Using density-functional theory, a large degree of crystal distortion by the bidentate mode of ligand chelation, and efficient ligand-NC electron transfer, synergistically resulting in the strongest CD signal (g-factor over 10-2) observed in chiral ligand-exchanged semiconductor NCs to date, is demonstrated. To demonstrate the effective chiral properties of these AgBiS2 NCs, a spin-filter device with over 86% efficiency is fabricated. This work represents a considerable leap in the field of chiral semiconductor NCs and points toward their future applications.

Suppressed Thermal Quenching via Tetrafluoroborate-Induced Surface Reconstruction of CsPbBr3 Nanocrystals for Efficient Perovskite Light-Emitting Diodes.

Although metal-halide perovskite nanocrystals (NCs) have garnered significant attention for optoelectronic applications, the presence of electrically insulating organic ligands in CsPbBr3 NCs hinders efficient charge injection and transportation in light-emitting diodes (LEDs). A common approach to address this issue involves ligand exchange with shorter ligands and precise control of the surface ligand density through additional purification steps. Nevertheless, the practical application of these methods has been hindered by their poor structural integrity and high surface-defect density, which remain a challenge. Our investigation reveals that NOBF4 treatment effectively replaces native ligands with BF4- anions, in which BF4- anions are readily coordinated with the positively charged CsPbBr3 surface metal centers, thereby improving the photoluminescence quantum yield (PLQY) and thermal stability. In particular, the presence of BF4- anions coordinated at CsPbBr3 surfaces efficiently suppresses the pathway of excitons toward thermally activated nonradiative recombination, leading to minimal thermal quenching and superior device performance in green-emitting PeLEDs. Notably, PeLEDs based on CsPbBr3 NCs with the reconstructed surface via NOBF4 treatment exhibit an improved current efficiency of 31.12 cd/A and an external quantum efficiency of 11.24%, increased by 2.8 times compared to that of the pristine sample, indicating the enhanced hole-electron injection and transport into the CsPbBr3 NCs. Therefore, our results highlight the potential of NOBF4 as a versatile reagent for the ligand exchange and surface passivation of CsPbBr3 NCs, thereby offering promising prospects for the development of stable, high-performance PeLEDs.

Colloidal Ag2SbBiSe4 nanocrystals as n‑type thermoelectric materials

Materials with low intrinsic thermal conductivity are essential for the development of high-performance thermoelectric devices. At the same time, the solution processing of these materials may enable the cost-effective production of the devices. Herein, we detail a high-yield and scalable colloidal synthesis route to produce Ag2SbBiSe4 nanocrystals (NCs) using amine-thiol-Se chemistry. The quaternary chalcogenide material is consolidated by a rapid hot-press maintaining the cubic crystalline structure. Transport measurements confirm that n-type Ag2SbBiSe4 exhibits an inherently ultralow lattice thermal conductivity of ca. 0.34 W m−1K−1 at 760 K. Moreover, a modulation doping strategy based on the blending of semiconductor Ag2SbBiSe4 and metallic Sn NCs is demonstrated to control the charge carrier concentration in the final composite material. The introduction of Sn nanodomains additionally blocks phonon propagation thus contributing to reducing the thermal conductivity of the final material. Ultimately, a peak thermoelectric figure of merit value of 0.64 at 760 K is achieved for n-type Ag2SbBiSe4-Sn nanocomposites that also demonstrate a notable Vickers hardness of 185 HV.