Iodotrimethylsilane as a Reactive Ligand for Surface Etching and Passivation of Perovskite Nanocrystals toward Efficient Pure-red to Deep-red LEDs

Resurfacing perovskite nanocrystals (NCs) with tight-binding and conductive ligands to resolve the dynamic ligands—surface interaction is the fundamental issue for their applications in perovskite light-emitting diodes (PeLEDs). Although various types of surface ligands have been proposed, these ligands either exhibit weak Lewis acid/base interactions or need high polar solvents for dissolution and passivation, resulting in a compromise in the efficiency and stability of PeLEDs. Herein, we report a chemically reactive agent (Iodotrimethylsilane, TMIS) to address the trade-off among conductivity, solubility and passivation using all-inorganic CsPbI₃ NCs. The liquid TMIS ensures good solubility in non-polar solvents and reacts with oleate ligands and produces in situ HI for surface etching and passivation, enabling strong-binding ligands on the NCs surface. We report, as a result, red PeLEDs with an external quantum efficiency (EQE) of ≈23 %, which is 11.2-fold higher than the control, and is among the highest CsPbI₃ PeLEDs. We further demonstrate the universality of this ligand strategy in the pure bromide system (CsPbBr₃), and report EQE of ≈20 % at 640, 652, and 664 nm. This represents the first demonstration of a chemically reactive ligand strategy that applies to different systems and works effectively in red PeLEDs spanning emission from pure-red to deep-red.     

Balancing the Rate of Cluster Growth and Etching for Gram‐Scale Synthesis of Thiolate‐Protected Au25 Nanoclusters with Atomic Precision

We report a NaOH‐mediated NaBH₄ reduction method for the synthesis of mono‐, bi‐, and tri‐thiolate‐protected Au₂₅ nanoclusters (NCs) with precise control of both the Au core and thiolate ligand surface. The key strategy is to use NaOH to tune the formation kinetics of Au NCs, i.e., reduce the reduction ability of NaBH₄ and accelerate the etching ability of free thiolate ligands, leading to a well‐balanced reversible reaction for rapid formation of thermodynamically favorable Au₂₅ NCs. This protocol is facile, rapid (≤3 h), versatile (applicable for various thiolate ligands), and highly scalable (>1 g Au NCs). In addition, bi‐ and tri‐thiolate‐protected Au₂₅ NCs with adjustable ratios of hetero‐thiolate ligands were easily obtained. Such ligand precision in molecular ratios, spatial distribution and uniformity resulted in richly diverse surface landscapes on the Au NCs consisting of multiple functional groups such as carboxyl, amine, and hydroxy. Analysis based on NMR spectroscopy revealed that the hetero‐ligands on the NCs are well distributed with no ligand segregation. The unprecedented synthesis of multi‐thiolate‐protected Au₂₅ NCs may further promote the practical applications of functional metal NCs.     

Controlled Growth of CH3NH3PbBr3 Perovskite Nanocrystals via a Water–Oil Interfacial Synthesis Method

Fundamental insights into the reaction kinetics of organic–inorganic lead halide perovskite nanocrystals (LHP NCs) are still limited due to their ultrafast formation rate. Herein, we develop a water–oil interfacial synthesis of MAPbBr₃ NCs (MA=CH₃NH₃⁺), which prolongs the reaction time to tens of minutes. This method makes it possible to monitor in situ the formation process of MAPbBr₃ NCs and observe successive spectral evolutions from 438 to 534 nm in a single reaction by extending reaction time. The implementation of this method depends on reducing the formation rate of PbBr₆^4? octahedra and the diffusion rate of MA. The formation of PbBr₆^4? is a rate‐determining step, and the biphasic system offers a favorable reaction condition to control the mass transfer of MA. The effects of temperature and concentration of precursor and ligand are investigated in detail.     

Improved Transversal Relaxivity for Highly Crystalline Nanoparticles of Pure γ‐Fe2O3 Phase

Pure and highly crystalline γ‐Fe₂O₃ nanocrystals (NCs) are obtained when hydrolysis and oxidation of a Fe^II organometallic precursor are performed in successive steps. Their synthesis in pure alkylamine leads to NCs of about 6 nm. In aqueous solutions of poly(vinyl)pyrrolidone, such pristine NCs form aggregates of about 150 nm that exhibit a high transversal relaxivity (r₂=466 mM ^?1 s^?1) about four times higher than that of a commercial Feridex magnetic resonance imaging (MRI) contrast agent. Consequently, they provide a significant decrease in the NMR signal at very short echo time (8 ms), which is of paramount importance in clinical practice because of the reduced duration of MRI measurements.     

Glycine-Functionalized CsPbBr3 Nanocrystals for Efficient Visible-Light Photocatalysis of CO2 Reduction

Capping ligands are indispensable for the preparation of metal-halide-perovskite (MHP) nanocrystals (NCs) with good stability; however, the long alkyl-chain capping ligands in conventional MHP NCs will be unfavorable for CO₂ adsorption and hinder the efficient carrier separation on the surface of MHP NCs, leading to inferior catalytic activity in artificial photosynthesis. Herein, CsPbBr₃ nanocrystals with short-chain glycine as ligand are constructed through a facile ligand-exchange strategy. Owing to the reduced hindrance of glycine and the presence of the amine group in glycine, the photogenerated carrier separation and CO₂ uptake capacity are noticeably improved without compromising the stability of the MHP NCs. The CsPbBr₃ nanocrystals with glycine ligands exhibit a significantly increased yield of 27.7 μmol g⁻¹ h⁻¹ for photocatalytic CO₂-to-CO conversion without any organic sacrificial reagents, which is over five times higher than that of control CsPbBr₃ NCs with conventional long alkyl-chain capping ligands.     

Spontaneous Crystallization of Perovskite Nanocrystals in Nonpolar Organic Solvents: A Versatile Approach for their Shape‐Controlled Synthesis

The growing demand for perovskite nanocrystals (NCs) for various applications has stimulated the development of facile synthetic methods. Perovskite NCs have often been synthesized by either ligand‐assisted reprecipitation (LARP) at room temperature or by hot‐injection at high temperatures and inert atmosphere. However, the use of polar solvents in LARP affects their stability. Herein, we report on the spontaneous crystallization of perovskite NCs in nonpolar organic media at ambient conditions by simple mixing of precursor–ligand complexes without application of any external stimuli. The shape of the NCs can be controlled from nanocubes to nanoplatelets by varying the ratio of monovalent (e.g. formamidinium⁺ (FA⁺) and Cs⁺) to divalent (Pb²⁺) cation–ligand complexes. The precursor–ligand complexes are stable for months, and thus perovskite NCs can be readily prepared prior to use. Moreover, we show that this versatile synthetic process is scalable and generally applicable for perovskite NCs of different compositions.     

Synthesis and green up-conversion fluorescence of colloidal La0.78Yb0.20Er0.02F3/SiO2 core/shell nanocrystals

Water-soluble PVP-stabilized hexagonal-phase La_0.78Yb_0.20Er_0.02F₃ nanocrystals (NCs) were synthesized by hydrothermal method. The NCs were coated with a very thin silica shell, and amino groups were introduced to the surface of silica shells by copolymerization of 3-aminopropyl(triethoxy)silane. The core/shell NCs can be dispersed in ethanol and water to form stable colloidal solution. The transmission electron microscopy (TEM), selected area electron diffraction (SAED), powder X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR) were used to characterize the core/shell materials. In addition, the green up-conversion fluorescence mechanism of La_0.78Yb_0.20Er_0.02F₃/SiO₂ NCs was studied with a 980-nm diode laser as excitation source. The water solubility, small core/shell particles size, and well colloidal stability mean the green up-conversion fluorescence NCs have potential applications in bioassay.     

Disclosing Interfaces of ZnO Nanocrystals Using Dynamic Nuclear Polarization: Sol‐Gel versus Organometallic Approach

The unambiguous characterization of the coordination chemistry of nanocrystal surfaces produced by wet‐chemical synthesis presently remains highly challenging. Here, zinc oxide nanocrystals (ZnO NCs) coated by monoanionic diphenyl phosphate (DPP) ligands were derived by a sol‐gel process and a one‐pot self‐supporting organometallic (OSSOM) procedure. Atomic‐scale characterization through dynamic nuclear polarization (DNP‐)enhanced solid‐state NMR (ssNMR) spectroscopy has notably enabled resolving their vastly different surface‐ligand interfaces. For the OSSOM‐derived NCs, DPP moieties form stable and strongly‐anchored μ₂‐ and μ₃‐bridging‐ligand pairs that are resistant to competitive ligand exchange. The sol‐gel‐derived NCs contain a wide variety of coordination modes of DPP ligands and a ligand exchange process takes place between DPP and glycerol molecules. This highlights the power of DNP‐enhanced ssNMR for detailed NC surface analysis and of the OSSOM approach for the preparation of ZnO NCs.     

Dopant-free NiOx Nanocrystals: A Low-cost and Stable Hole Transport Material for Commercializing Perovskite Optoelectronics

Advancing inverted (p-i-n) perovskite solar cells (PSCs) is critical for commercial applications given their compatibility with different bottom cells for tandem photovoltaics, low-temperature processability (≤100 °C), and promising operational stability. Although inverted PSCs have achieved an efficiency of over 25 % using doped or expensive organic hole transport materials (HTMs), their synthesis cost and stability still cannot meet the requirements for their commercialization. Recently, dopant-free and low-cost non-stoichiometric nickel oxide nanocrystals (NiO_x NCs) have been extensively studied as a low-cost and effective HTM in perovskite optoelectronics. In this minireview, we summarize the synthesis and surface-functionalization methods of NiO_x NCs. Then, the applications of NiO_x NCs in other perovskite optoelectronics beyond photovoltaics are discussed. Finally, we provide a perspective for the future development of NiO_x NCs for the commercialization of perovskite optoelectronics.     

Impact of Zn-doping on the composition,stability, luminescence properties of silica coated all-inorganic cesium lead bromide nanocrystals and their biocompatibility

Cesium lead halide (CsPbX₃: X = I, Br, Cl) nanocrystals (NCs) are believed to be potential candidates for bioimaging applications. However, their low structural stability against polar solvents remains as a major limitation. To improve the NCs stability and maintain high emission intensity, we synthesized silica coated Zn-doped core@shell perovskite NCs via modified ligand assisted reprecipitation (LARP) synthetic method under relatively high humid condition. We systemically varied the composition inside the perovskite structure and then studied their photophysical properties and stability. Interestingly, the Zn-doping amount controls the ratio of CsPbBr₃ to Cs₄PbBr₆ perovskites inside the core and also facilitates the growth of (OA)₂PbBr₄ shell, enables overall increase in NCs emission intensity and stability. We observed green color emission from these NCs in the spectral range of 494-506 nm with a maximum photoluminescence quantum yield (PLQY) up to 88%. The optimized Zn-doped NCs exhibited nearly four times better water stability compared to the bare NCs and retain emission properties for several months even in highly polar solvents. Finally, we performed biocompatibility test of the NCs generated on biological samples and hydroponics test in a gardenia leaf for their potential bioimaging applications.     

Probing defect-originated properties,actinide-lanthanide doping,and gamma irradiation effect in Lu2Hf2O7 pyrochlore nanocrystals for phosphor and nuclear applications

Multifunctional materials are in high demand these days by virtue of their efficacy to perform more than one role and are expected to ease the high global materials crunch. This work is directed towards probing defect emission in undoped and doping of uranium (U), plutonium (Pu), curium (Cm), cerium (Ce), and samarium (Sm) Lu₂Hf₂O₇ (LuHO) pyrochlore nanocrystals (NCs) for photoluminescence and radioactive waste immobilization. Density of state calculations shows abundant defects in the undoped LuHO NCs. Multiple visible luminescence spanning violet to red in the undoped LuHO pyrochlore NCs upon ultraviolet irradiation was ascribed to the presence of neutral and ionized oxygen vacancies. The doped LuHO NCs show typical blue (Ce³⁺), orange-red (Sm³⁺), and green (U⁶⁺) emissions endowed by 4f→5d, 4f→4f, and charge transfer transitions, respectively. Moreover, uranium is stabilized as UO₆^6? ion (octahedral uranate) in the LuHO pyrochlore lattice. Luminescence lifetime spectroscopy and density functional theory (DFT) calculated defect formation energies suggest that Ce, Sm, Cm, and Pu ared stabilized at Lu³⁺ site whereas U is stabilized at Hf⁴⁺ site in the LuHO NCs. The LuHO pyrochlore NCs also demonstrate high radiation stability on gamma exposure retaining the crystallinity and undergoing structural phase transition from defect fluorite to ideal pyrochlore structure. Considering the significant health hazard posed by radioactive elements present in the spent fuel, these LuHO NCs possess high potential to immobilize U, Pu, Cm, Ce, and Sm. This work poses high significance for immobilizing radioactive nuclear waste and designing tunable luminescent solid-state NCs.     

Lead‐Free,Air‐Stable All‐Inorganic Cesium Bismuth Halide Perovskite Nanocrystals

Lead‐based perovskite nanocrystals (NCs) have outstanding optical properties and cheap synthesis conferring them a tremendous potential in the field of optoelectronic devices. However, two critical problems are still unresolved and hindering their commercial applications: one is the fact of being lead‐based and the other is the poor stability. Lead‐free all‐inorganic perovskite Cs₃Bi₂X₉ (X=Cl, Br, I) NCs are synthesized with emission wavelength ranging from 400 to 560 nm synthesized by a facile room temperature reaction. The ligand‐free Cs₃Bi₂Br₉ NCs exhibit blue emission with photoluminescence quantum efficiency (PLQE) about 0.2 %. The PLQE can be increased to 4.5 % when extra surfactant (oleic acid) is added during the synthesis processes. This improvement stems from passivation of the fast trapping process (2–20 ps). Notably, the trap states can also be passivated under humid conditions, and the NCs exhibited high stability towards air exposure exceeding 30 days.     

Lead‐Free,Air‐Stable All‐Inorganic Cesium Bismuth Halide Perovskite Nanocrystals

Lead‐based perovskite nanocrystals (NCs) have outstanding optical properties and cheap synthesis conferring them a tremendous potential in the field of optoelectronic devices. However, two critical problems are still unresolved and hindering their commercial applications: one is the fact of being lead‐based and the other is the poor stability. Lead‐free all‐inorganic perovskite Cs₃Bi₂X₉ (X=Cl, Br, I) NCs are synthesized with emission wavelength ranging from 400 to 560 nm synthesized by a facile room temperature reaction. The ligand‐free Cs₃Bi₂Br₉ NCs exhibit blue emission with photoluminescence quantum efficiency (PLQE) about 0.2 %. The PLQE can be increased to 4.5 % when extra surfactant (oleic acid) is added during the synthesis processes. This improvement stems from passivation of the fast trapping process (2–20 ps). Notably, the trap states can also be passivated under humid conditions, and the NCs exhibited high stability towards air exposure exceeding 30 days.     

Ultrasensitive photoelectrochemical sensing of nicotinamide adenine dinucleotide based on graphene-TiO2 nanohybrids under visible irradiation

In this paper, the photoelectrochemical behavior of graphene-TiO₂ (G-TiO₂) nanohybrids was investigated in the visible region and a new photoelectrochemical sensor for sensitive determination of nicotinamide adenine dinucleotide (NADH) was proposed. Under visible light, the G-TiO₂ nanohybrids possessed enhanced photocurrent, which was nearly 5 times than that of pure TiO₂ nanocrystals (NCs). Based on the enhanced photocurrent of G-TiO₂ nanohybrids toward NADH, a new photoelectrochemical methodology for ultrasensitive determination of NADH was developed. The proposed sensor showed linearly enhanced photocurrent by increasing the NADH concentration from 1.0 × 10⁻⁸ to 2.0 × 10⁻³ M with a low detection limit of 3.0 × 10⁻⁹ M. Furthermore, this sensor exhibited good selectivity and stability towards NADH determination. This strategy opens up a new avenue for the application of graphene-based hybrids in the field of photoelectrochemical sensing and monitoring.     

Completely Green Synthesis of Colloid Adams’ Catalyst α‐PtO2 Nanocrystals and Derivative Pt Nanocrystals with High Activity and Stability for Oxygen Reduction

We report a first solution strategy for controlled synthesis of Adams’ catalyst (i.e., α‐PtO₂) by a facile and totally green approach using H₂PtCl₆ and water as reactants. The prepared α‐PtO₂ nanocrystals (NCs) are ultrasmall in size and have very “clean” surfaces, which can be reduced to Pt NCs easily in ethanol under ambient conditions. Such Adams’ catalysts have been applied as electrocatalysts beyond the field of heterogeneous catalysis. Noticeably, the water‐only synthesized α‐PtO₂ NCs and their derivative Pt NCs all exhibit much higher oxygen reduction reaction (ORR) activities and stabilities than that of the state‐of‐art Pt/C electrocatalysts. This study provides an example on the organics‐free synthesis of α‐PtO₂ and Pt NCs as promising cathode catalysts for fuel cell applications and, particularly, this simple, straightforward method may open a new way for the synthesis of other “clean” functional nanomaterials.     

Poly(ethylene glycol)-based multidentate oligomers for biocompatible semiconductor and gold nanocrystals

We have developed a new set of multifunctional multidentate OligoPEG ligands, each containing a central oligomer on which were laterally grafted several short poly(ethylene glycol) (PEG) moieties appended with either thioctic acid (TA) or terminally reactive groups. Reduction of the TAs (e.g., in the presence of NaBH(4)) provides dihydrolipoic acid (DHLA)-appended oligomers. Here the insertion of PEG segments in the ligand structure promotes water solubility and reduces nonspecific interactions, while TA and DHLA groups provide multidentate anchoring onto Au nanoparticles (AuNPs) and ZnS-overcoated semiconductor quantum dots (QDs), respectively. The synthetic route involves simple coupling chemistry using N,N-dicylohexylcarbodiimide (DCC). Water-soluble QDs and AuNPs capped with these ligands were prepared via cap exchange. As prepared, the nanocrystals dispersions were aggregation-free, homogeneous, and stable for extended periods of time over pH ranging from 2 to 14 and in the presence of excess electrolyte (2 M NaCl). The new OligoPEG ligands also allow easy integration of tunable functional and reactive groups within their structures (e.g., azide or amine), which imparts surface functionalities to the nanocrystals and opens up the possibility of bioconjugation with specific biological molecules. The improved colloidal stability combined with reactivity offer the possibility of using the nanocrystals as biological probes in an array of complex and biologically relevant media.     

Shape tunable two−dimensional ligand−free cesium antimony chloride perovskites

Organic ligands play a key role in determining the shape and stability of the perovskite nanocrystals (NCs). However, the ligands often create poor stability and defects through imperfect attachment, in addition to the post synthesis detachment. We developed a novel route to synthesize the ligand?free ambient stable two?dimensional (2D) cesium antimony chloride (Cs₃Sb₂Cl₉) NCs. First, hexagonal shape NCs are synthesized through a fast one?step reaction at room temperature using a reprecipitation method. The shape of hexagonal NCs is further tuned into well?defined 2D plates through a solid-state temperature-driven crystal phase transition. In?situ variable temperature X?ray diffraction and differential scanning calorimetry cycles probe temperature-sensitive metastability and irreversibility of trigonal to orthorhombic crystallographic phase transition. Rietveld analyses quantify volume fractions and coherently diffracting crystallite domains that promote the growth of the two crystal phases. Both the hexagonal NCs and plates show ambient structural stability for over months. The proposed formation mechanism can guide to improve synthetic methods to realize ligand?free shape-controlled perovskite NCs.     

Controllable synthesis of ZnS/PMMA nanocomposite hybrids generated from functionalized ZnS quantum dots nanocrystals

We reported controllable synthesis of ZnS nanocrystal-polymer transparent hybrids by using polymethylmethacrylate (PMMA) as a polymer matrix. In a typical run, the appropriate amounts of zinc chloride (ZnCl₂) and sodium sulfide (Na₂S) in the presence of 2-mercaptoethanol (ME) as the organic ligand were well dispersed in H₂O/dimethylformamide solution without any aggregation. In addition, the Mn-doped ZnS nanocrystals (NCs) were synthesized with similar method. Then, ZnS-PMMA hybrids were obtained via free radical polymerization in situ by using ZnS NCs functionalized with methacryloxypropyltrimethoxysilane (MPS). FT-IR characterization indicates the formation of robust bonding between ZnS NCs and the organic ligand. The TEM images show that ZnS NCs are well dispersed in PMMA matrix, and particle size of as-prepared ZnS NCs is about 2.6 nm, in agreement with the computing results of Brus’s model and Debye–Scherrer formula. The photoluminescence measurements present that ZnS NCs, Mn-doped ZnS NCs, and ZnS/PMMA hybrid show good optical properties.     

Comparative Structural,Optical, and Photoluminescence Studies of YF3:Pr,YF3:Pr@LaF3, and YF3:Pr@LaF3@SiO2 Core–Shell Nanocrystals

Praseodymium (Pr³⁺)‐doped YF₃ (core) and LaF₃ ‐covered YF₃ :Pr (core–shell) nanocrystals (NCs ) were prepared successfully by an ecofriendly, polyol‐based, co‐precipitation process, which were then coated with a silica shell by using a sol–gel‐based Stober method. X‐ray diffraction (XRD), transmission electron microscopy (TEM ), thermal analysis, Fourier transform infrared (FTIR) , UV /vis, energy bandgap, and photoluminescence studies were used to analyze the crystal structure, morphology, and optical properties of the nanomaterial. XRD and TEM results show that the grain size increases after sequential growth of crystalline LaF₃ and the silica shell. The silica surface modification enhances the solubility and colloidal stability of the core–shell‐SiO₂ NCs . The results indicate that the surface coating affects the optical properties because of the alteration in crystalline size of the materials. The emission intensity of silica‐modified NCs was significantly enhanced compared to that of core and core–shell NCs . These results are attributed to the formation of chemical bonds between core–shell and noncrystalline SiO₂ shell via La–O–Si bridges, which activate the “dormant” Pr³⁺ ions on the surfaces of the nanoparticles. The luminescence efficiency of the as‐prepared core, core–shell, and core–shell‐SiO₂ NCs are comparatively analyzed, and the observed differences are justified on the basis of the surface modification surrounding the luminescent seed core NCs .     

Greatly enhanced electrochemiluminescence of CdS nanocrystals upon heating in the presence of ammonia

CdS nanocrystals (NCs) usually exhibit very weak electrochemiluminescence (ECL) emission. It is showed that when CdS NCs were treated by heating in the presence of ammonia (heated-CdS–NH₃), greatly enhanced ECL was observed. The ECL of the heated-CdS–NH₃ modified glassy carbon electrode (heated-CdS–NH₃/GCE) in phosphate buffer solution (pH 7.0) containing 0.1 M K₂S₂O₈ was ca. 310 times higher than that of CdS/GCE. The treatment caused the changes in the morphology and surface electronic structure of CdS NCs, which facilitated the reduction process of CdS, consequently improved the quantity of the excited states (CdS*), leading to enormous enhancement in ECL.