Stability Of Nanocrystals Research Articles

Low-temperature liquid-phase formation of environmentally stable copper halide nanocrystal superlattices and their application to anticounterfeiting patterns

Nanocrystal superlattices have the potential to create a new class of semiconductor materials by combining the photophysical properties of individual nanocrystals with bulk-like structure performance. However, the principles underlying the direct formation of superlattices in liquid phase have not been thoroughly investigated, particularly, those consisting of exciton self-trapping metal halides. Here, we explore the formation of Cs3Cu2Br5 nanocrystal superlattices via liquid-phase crystallization of growing nanocrystals over a reaction period of only a few seconds. Importantly, the reaction temperature and the precursor concentration were found to be key parameters governing the concomitant nanocrystal growth and superlattice formation. The resulting Cs3Cu2Br5 superlattices had a well-defined face-centered cubic structure and emitted a single-band bright blue emission when exposed to 280 nm light. Owing to their advantages, such as low toxicity, reabsorption-free, narrow absorption, strong emission, and high environmental stability, the Cs3Cu2Br5 superlattices were applicable to anti-counterfeiting applications. Our findings shed light on the liquid-phase assembly of nanocrystals into superlattices and highlight the potential applications of the superlattices.

Effect of Al Segregation on Mechanical Properties and Deformation Mechanism of Nanocrystalline NiCoAl

Solute element segregation behavior significantly changes the mechanical properties and deformation mechanism of nanocrystals. In this work, we studied the effect of segregation structure on the deformation mechanism of NiCoAl nanocrystalline by molecular dynamics. The results show that the grain boundary stability of nanocrystals is the worst when Al is completely segregated within the grain, and the metastable grain boundary cannot effectively hinder the dislocation movement, resulting in poor mechanical properties of nanocrystals. When 4% of Al transitioned to the grain boundary, the grain boundary stability was greatly improved and many lamination structures were generated. At this time, the lamination structure and stable grain boundaries were effectively nailed to dislocations, resulting in nanocrystal strengthening. With the complete segregation of Al at the grain boundary, the grain boundary shows a stable ability significantly and inhibits the nucleation of dislocation, leading to a decline in the strength of nanocrystals. In this effort, the deformation mechanism of solute element segregation is investigated from the interaction of dislocation and solid solution element, which is conducive to the design of advanced materials with excellent properties. Our work provides fascinating insights into the mechanism of plastic deformation response under solute element segregation structure.

Design Principle of a Water-Dispersed Photocatalytic Perovskite through Ligand Deconstruction

Strategically designed surface modifiers that produce stable perovskite nanocrystals (NCs) and allow efficient charge extraction in polar solvents are critical for perovskite photocatalysis. We designed a multifunctional bolaamphiphilic ligand (NKE-12) with multidentate ionic groups at both ends, which significantly increases the colloidal stability of CsPbBr3 NCs in an aqueous medium without affecting their structural integrity and catalytic attributes. Ligand deconstruction via K and E fragmented ligands revealed synergistic actions of the cationic and anionic functionalities in surface passivation, phase separation, and water localization away from the surface of NKE-12-modified CsPbBr3 NCs. Multidimensional nuclear magnetic resonance experiments and contact angle measurements further suggested surface interactions and improved hydrophilicity via ionic terminal groups that account for water stability. Photogenerated hole-transfer dynamics of CsPbBr3/NKE-12 NCs to a probe molecule 6,7-dihydroxycoumarin was studied using transient absorption spectroscopy. Overall, this study paves the way for ligand design principles for surface engineering to develop water-stable perovskite photocatalysts.

Bis(stearoyl) Sulfide: A Stable, Odor‐Free Sulfur Precursor for High‐Efficiency Metal Sulfide Quantum Dot Photovoltaics

AbstractThe synthesis of metal sulfide nanocrystals is a crucial step in the fabrication of quantum dot (QD) photovoltaics. Control over the QD size during synthesis allows for precise tuning of their optical and electronic properties, making them an appealing choice for electronic applications. This flexibility has led to the implementation of QDs in both highly‐efficient single junction solar cells and other optoelectronic devices including photodetectors and transistors. Most commonly, metal sulfide QDs are synthesized using the hot‐injection method utilizing a toxic, and air‐ and moisture‐sensitive sulfur source: bis(trimethylsilyl) sulfide ((TMS)2S). Here, bis(stearoyl) sulfide (St2S) is presented as a new type of air‐stable sulfur precursor for the synthesis of sulfide‐based QDs, which yields uniform, pure, and stable nanocrystals. Photovoltaic devices based on these QDs are equally efficient as those fabricated by (TMS)2S but exhibit enhanced operational stability. These results highlight that St2S can be widely adopted for the synthesis of metal sulfide QDs for a range of optoelectronic applications.

Engineering highly fluorescent and colloidally stable CsPbBr3 nanocrystals of different shapes using imidazolium-based polysalt ligands

Engineering highly fluorescent and colloidally stable CsPbBr3 nanocrystals of different shapes using imidazolium-based polysalt ligands

Enhanced stability of CsPbI3 nanocrystals by ethylenediammonium diiodide

Enhanced stability of CsPbI3 nanocrystals by ethylenediammonium diiodide

Energy and Charge Transfer Dynamics in Red-Emitting Hybrid Organo-Inorganic Mixed Halide Perovskite Nanocrystals.

We report time-resolved spectral properties of highly stable and efficient red-emitting hybrid perovskite nanocrystals with the composition FA0.5MA0.5PbBr0.5I2.5 (FAMA PeNC) synthesized by using the hot-addition method. The PL spectrum of the FAMA PeNC shows a broad asymmetric band covering 580 to 760 nm with a peak at 690 nm which can be deconvoluted into two bands corresponding to the MA and FA domains. The interactions between the MA and FA domains are shown to affect the relaxation dynamics of the PeNCs from the subpicosecond to tens of nanoseconds scale. Time-correlated single-photon counting (TCSPC), femtosecond PL optical gating (FOG), and femtosecond transient absorption spectral (TAS) techniques were employed to study the intercrystal energy transfer (photon recycling) and intracrystal charge transfer processes between the MA and the FA domains of the crystals. These two processes are shown to increase the radiative lifetimes for the PLQYs exceeding 80%, which may play a key role in enhancing the performance of PeNC-based solar cells.

Stable CsPbX3 (X = Cl, Br, I) Nanocrystal‐in‐Glass Composite (NGC) for Solid‐State Laser‐Driven White Light Generation

AbstractPerovskite CsPbX3 (X = Cl, Br, I) nanocrystals with advantages of high quantum yield, narrow emission peaks, and tunable fluorescence are considered as the next generation of light‐emitting sources. However, fluorescence degradation due to the poor stability of perovskite nanocrystals in moisture, high temperature, and illumination remains one of the greatest challenges in their further development. In this work, a fully dense coating strategy is proposed to improve the overall stability of perovskite nanocrystals, especially under high‐density laser irradiation. A mesoporous silica SiO2 layer is introduced to construct a stable coating for isolating the perovskite from external environment. To eliminate the pores of the CsPbX3@SiO2, an inorganic glass is also employed via solution‐combustion technique to generate a fully compact encapsulation for further stability promotion. The as‐prepared nanocrystal‐in‐glass composite exhibits efficient and stable fluorescence performance in luminous efficiency, chromaticity, and long‐term reliability in the conditions of thermal shock, humidity, and blue laser irradiation. With the integration of red/green/blue emitting nanocrystals, the color gamut of the white laser lighting source covers 134% of the National Television Standards Committee standard, providing exciting opportunity for high performance laser‐driven white light generation.

Pickering emulsion co‐stabilised by cellulose nanocrystals and astragalin/tangeretin: effect of environmental factors

SummaryThis study aims to reveal the stability of cellulose nanocrystals (CNCs) and astragalin/tangeretin co‐stabilised Pickering emulsion under different environmental factors such as ionic strengths, pH values, thermal treatment, freeze–thaw treatment, sodium ascorbate, and storage condition. Results showed that the astragalin and CNCs co‐stabilised Pickering emulsion (AST‐CPE) could maintain a stable appearance, typical spherical morphology droplets, and steady physical stability under various conditions, including ionic strength at low 20 mm, pH values 2–8, thermal treatment (65, 85, and 135 °C), the addition of sodium ascorbate, and storage at 4 °C for 35 days. It is noteworthy that AST‐CPE showed higher emulsion physical stability at pH 2 (56.67%) and pH 8 (53.33%). The co‐stabilised Pickering emulsion structure has a firm and physically stable system. Moreover, it could effectively protect the bioactive substance by expanding its application in food delivery vehicles.

Highly Stable CsPbBr3 Perovskite Nanocrystals Encapsulated in Metal–Organic Frameworks for White Light-Emitting Diodes

CsPbX3 (X = Cl, Br, I) perovskite nanocrystals (NCs) have shown great potential in numerous applications including wide color gamut display and lighting. Despite the wonderful luminescence properties, the inherent instability of these NCs hinders their use in practical situations. Herein, we report a facile aqueous-based, ligand-free method to synthesize highly stable CsPbX3 NCs using ZIF-62, a metal–organic framework, as an encapsulation matrix which effectively isolates CsPbX3 from the surrounding. We discovered that the slightly alkaline nature of ZIF-62 facilitates the reaction between water and PbBr2 to form PbBr(OH), which not only passivates the surface defects of the CsPbBr3 NCs but also prevents the perovskite from decomposing or oxidizing at high temperature. Sintering of ZIF-62 can therefore be performed in air at ∼300 °C to completely seal the perovskite within the insulating matrix, resulting in CsPbBr3/ZIF-62 composites exhibiting high stability against polar solvents, heat, light, and ambient humidity. Notably, the composite can maintain its bright luminescence without noticeable degradation in water for more than 2 months. The narrow-band emission and stability of these composites led to the demonstration of white light-emitting diodes with excellent color stability. Without the need for organic solvents during NC synthesis and noble gas ambient during sintering, the strategy proposed here can potentially facilitate the cost-effective, large-scale synthesis of highly stable perovskites which show great promise in commercial applications.

Multi-color UCNPs/CsPb(Br1-xIx)3 for upconversion luminescence and dual-modal anticounterfeiting.

Advanced hybrid materials have attracted extensive attention in optoelectronics and photonics application due to their unique and excellent properties. Here, the multicolor upconversion luminescence properties of the hybrid materials composed of CsPbX3(X = Br/I) perovskite quantum dots and upconversion nanoparticles (UCNPs, core-shell NaYF4:25%Yb3+,0.5%Tm3+@NaYF4) is reported, achieving the upconversion luminescence with stable and bright of CsPbX3 perovskite quantum dots under 980 nm excitation. Compared with the nonlinear upconversion of multi-photon absorption in perovskite, UCNPs/CsPbX3 achieves lower power density excitationby using theUCNPs as the physical energy transfer level, meeting the demand for multi-color upconversion luminescence in optical applications. Also, the UCNPs/CsPbX3 combined with ultraviolet curable resin (UVCR) shows excellent water and air stability, which can be employed as multicolor fluorescent ink for screen printing security labels. Through the conversion strategy, the message of the security labels can be encrypted and decrypted by using UV light and a 980 nm continuous wave excitation laser as a switch, which greatly improves the difficulty of forgery. These findings provide a general method to stimulate photon upconversion and improve the stability of perovskite nanocrystals, which will be better applied in the field of anti-counterfeiting.

High photoactive black phase stability of CsPbI3nanocrystals under damp-heat conditions of 85 °C and 85% relative humidity

High damp-heat stability of CsPbI3nanocrystals is demonstrated by B-site ion doping engineering. The black phase stability time of these nickel ion doped nanocrystals reaches a record 54 hours under the conditions of 85 °C and 85% relative humidity.

Magnetic Nanoplatform With Novel Potential for the Treatment of Bone Pathologies: Drug Loading and Biocompatibility on Blood and Bone Cells.

Magnetic iron oxide nanoparticles (MNPs) coated with citric acid (MG@CA) are proposed as raw materials for the treatment of bone diseases. Citric acid (CA) was selected as coating due to its role in the stabilization of apatite nanocrystals and as a signaling agent for osteoblast activation. Raloxifene (Ral), curcumine (Cur) and methylene blue (MB) were employed as model drugs as therapeutic agents for bone diseases. Characterization of raw and drug loaded nanosystems was conducted in order to elucidate the mechanisms governing interactions between therapeutics and the magnetic platform. Biocompatibility studies were performed on red blood cells (RBCs) from peripheral human blood. Cytotoxicity was evaluated on endothelial cells (ECs); and viability was studied for bone cells exposed at concentrations of 1, 10 and 100 [Formula: see text]/mL of the magnetic nano-platform. MG@CA exhibited proper physicochemical properties for the applications intended within this work. It presented satisfactory biocompatibility on peripheral red blood cells. Only doses of 100 [Formula: see text]/mL induced a decrease in metabolic activity of ECs and MC3T3-E1 cells. Drug adsorption efficiency was estimated as 62.0, 15.0 and 54.0 % for Ral, Cur and MB and drug loading capability of 12.0, 20.0 and 13.6%, respectively.

Preparation and formation process of high efficient and stable CsPbBr<sub>3</sub>-Cs<sub>4</sub>PbBr<sub>6</sub> nanocrystals with mixed phase

CsPbBr<sub>3</sub>-Cs<sub>4</sub>PbBr<sub>6</sub> dual-phase nanocrystals are prepared by adding the mixture ligand of oleylamine and tetradecyl-phosphonic acid (OLA-TDPA) to CsPbBr<sub>3</sub> perovskite nanocrystals through ligand post-treatment. The structure, the morphology, optical property and the stability of CsPbBr<sub>3</sub>-Cs<sub>4</sub>PbBr<sub>6</sub> dual-phase nanocrystals are characterized by X-ray diffraction, transmission electron microscopy (high-resolution TEM), UV-vis spectrophotometer, fluorescence spectrophotometer, and transient fluorescence spectrophotometer. The as-obtained nanocrystals have a high photoluminescence quantum yield of 78% and long fluorescence lifetime of 476 ns when prepared at the optimal molar ratio of CsPbBr<sub>3</sub>, TDPA and OLA (1∶1∶15). Moreover, the nanocrystal is quite stable at room temperature for at least 25 days, and has a good thermal stability in five heating-cooling cycles at temperature in a range between 293 K and 328 K. The formation of dual-phase nanocrystals go through two stages of surface passivation/dissolution and recrystallization to generate CsPbBr<sub>3</sub>-Cs<sub>4</sub>PbBr<sub>6</sub> nanocrystals. In the first stage (<i>t</i> ≤ 1 h), the m OLA-TDPA mixing ligand can form (RNH<sub>3</sub>)<sub>2</sub>PO<sub>3</sub> X type ligand and exchanges with [RNH<sub>3</sub>]<sup>+</sup>-[RCOO]<sup>–</sup> at the surface of CsPbBr<sub>3</sub> nanocrystals, which can effectively passivate surface defects by strong interaction with Pb<sup>2+</sup> and high ligand content at surface, thus improving the quantum yield and fluorescence life of CsPbBr<sub>3</sub> nanocrystals with spherical shape. In the second stage, with the increase of reaction time, PbBr<sub>2</sub> partially dissolves from the surface of CsPbBr<sub>3</sub> nanocrystals, then some CsPbBr<sub>3</sub> nanocrystals transform into lead-depleted Cs<sub>4</sub>PbBr<sub>6</sub> nanocrystals with hexagonal phase, thus improving the stability of nanocrystals. This work has a certain reference value for promoting the applications of high efficient and stable perovskite nanocrystals.

Polymeric ionic liquid-based formulations for the fabrication of highly stable perovskite nanocrystal composites for photocatalytic applications.

Halide perovskite nanocrystals (PNCs) have emerged as potential visible-light photocatalysts because of their outstanding intrinsic properties, including high absorption coefficient and tolerance to defects, which reduces non-radiative recombination, and high oxidizing/reducing power coming from their tuneable band structure. Nevertheless, their sensitivity to humidity, light, heat and water represents a great challenge that limits their applications in solar driven photocatalytic applications. Herein, we demonstrate the synergistic potential of embedding PNCs into polymeric ionic liquids (PILs@PS) to fabricate suitable composites for photodegradation of organic dyes. In this context, the stability of the PNCs after polymeric encapsulation was enhanced, showing better light, moisture, water and thermal stability compared to pristine PNCs for around 200 days.

Photosensitisation of inkjet printed graphene with stable all-inorganic perovskite nanocrystals.

All-inorganic perovskite nanocrystals (NCs) with enhanced environmental stability are of particular interest for optoelectronic applications. Here we report on the formulation of CsPbX3 (X is Br or I) inks for inkjet deposition and utilise these NCs as photosensitive layers in graphene photodetectors, including those based on single layer graphene (SLG) as well as inkjet-printed graphene (iGr) devices. The performance of these photodetectors strongly depends on the device structure, geometry and the fabrication process. We achieve a high photoresponsivity, R > 106 A W-1 in the visible wavelength range and a spectral response controlled by the halide content of the perovskite NC ink. By utilising perovskite NCs, iGr and gold nanoparticle inks, we demonstrate a fully inkjet-printed photodetector with R ≈ 20 A W-1, which is the highest value reported to date for this type of device. The performance of the perovskite/graphene photodetectors is explained by transfer of photo-generated charge carriers from the perovskite NCs into graphene and charge transport through the iGr network. The perovskite ink developed here enabled realisation of stable and sensitive graphene-based photon detectors. Compatibility of inkjet deposition with conventional Si-technologies and with flexible substrates combined with high degree of design freedom provided by inkjet deposition offers opportunities for partially and fully printed optoelectronic devices for applications ranging from electronics to environmental sciences.

Recent advances in encapsulation of highly stable perovskite nanocrystals and their potential applications in optoelectronic devices.

Due to their tunable wavelength, high color purity, bright emission and low-cost fabrication process, perovskite nanocrystals (PeNCs) have attracted broad interest and exhibited great prospects in application areas such as solar cells, light-emitting diodes, photodetectors, and lasers. Although the fabrication of PeNCs and related optoelectronic devices has witnessed rapid development over the past several years, the poor stability of PeNCs in an external environment still remains a major drawback which severely limits the further improvement and commercialization of PeNC-based devices. Therefore, various techniques and strategies have been developed to enhance the stability of PeNCs. Among them, the encapsulation strategy has been demonstrated to be an effective way to improve the stability of PeNCs. In this review, the origin of the instability of PeNCs is first analyzed to identify the importance of encapsulation, followed by a summary and discussions on recent advances in the encapsulation of PeNCs. The potential applications of encapsulated PeNCs in various optoelectronic devices are also presented to manifest the necessity of encapsulation. Finally, the further development and outlook on encapsulation of PeNCs are analyzed in order to suggest future improvements and commercialization of PeNCs and related optoelectronic devices.

Ligand-free template-assisted synthesis of stable perovskite nanocrystals with near-unity photoluminescence quantum yield within the pores of vaterite spheres.

Ligand-free methods for the synthesis of halide perovskite nanocrystals are of great interest because of their excellent performance in optoelectronics and photonics. In addition, template-assisted synthesis methods have become a powerful tool for the fabrication of environmentally stable and bright nanocrystals. Here we develop a novel approach for the facile ligand-free template-assisted fabrication of perovskite nanocrystals with a near-unity absolute quantum yield, which involves CaCO3 vaterite micro- and submicrospheres as templates. We show that the optical properties of the obtained nanocrystals are affected not mainly by the template morphology, but strongly depend on the concentration of precursor solutions, anion and cation ratio, as well as on adding defect-passivating rare-earth dopants. The optimized samples are further tested as infrared radiation visualizers exhibiting promising characteristics comparable to those that are commercially available.

Stable and luminescent cesium copper halide nanocrystals embedded in flexible polymer fibers for fabrication of down-converting WLEDs.

Recently, CsPbX3 (X = I, Br, Cl) perovskite nanocrystals (NCs) have drawn wide attention owing to their outstanding photophysical and optoelectronic properties. However, the toxicity of such NCs remained a big challenge for further commercialization. Herein, we adopt facile methods for synthesizing green-emissive Cs3Cu2Cl5 and blue-emissive Cs3Cu2Br2.5I2.5 perovskite NCs that exhibit broad emission spectra with large Stokes shifts. These NCs showed photoluminescence quantum yields (PLQY) up to 65% (Cs3Cu2Cl5 NCs) and 32% (Cs3Cu2Br2.5I2.5 NCs) with limited stabilities. To further improve the stability, the NCs were blended with a hydrophobic polymer poly-methylmethacrylate (PMMA) and embedded inside the polymer fiber by an electrospinning process to form composite fibers. The as-prepared Cs3Cu2Cl5@PMMA and Cs3Cu2Br2.5I2.5@PMMA fiber films demonstrated good surface coverage and better thermal stability, and even retained their emission properties when dispersed in water. The emissive fibers were also deposited on flexible polyethylene terephthalate (PET) substrates that displayed high resistance towards bending and twisting with no signs of breakage, damage, or loss of optical properties. Finally, UV-pumped phosphor-converted WLEDs fabricated by using these blue and green-emitting fibers revealed CIE chromaticity coordinates at (0.27, 0.33) with a maximum luminous efficiency of 69 Lm W-1 and correlated color temperature (CCT) value of 8703 K. These outcomes can be beneficial for the development of futuristic flexible display technologies.

Uniform nucleation and growth of Cs3Cu2I5 nanocrystals with high luminous efficiency and structural stability and their application in white light-emitting diodes.

Copper-based ternary halide composites have attracted great attention due to their superior chemical stability and optical properties. Herein, we developed an ultrafast high-power ultrasonic synthesis strategy to realize the uniform nucleation and growth of highly luminescent and stable Cs3Cu2I5 nanocrystals (NCs). The as-synthesized Cs3Cu2I5 NCs show uniform hexagonal morphology with an average mean size of 24.4 nm and emit blue light with a high photoluminescence quantum yield (PLQY) of ∼85%. Moreover, the Cs3Cu2I5 NCs exhibit a remarkable stability during continuous eight times heating/cooling cycling tests (303-423 K). We also demonstrated an efficient and stable white light-emitting diode (WLED) with a high luminous efficiency (LE) of 41.5 lm W-1 and a Commission Internationale de l'Eclairage (CIE) color coordinate of (0.33,0.33).