Magnetic modulation on chiroptical activities of nematically assembled carbon dots.

Effectively harnessing the assembly of achiral carbon dots into a chiral manner is a prominent step for applying carbon dots into the area of stereoselective optoelectronics and theranostics. Herein, magnetic-modulated and circularly polarized luminescence (CPL)-active photonic thin films were presented in this article via co-assembly and magnetic-mediation strategy of cellulose nanocrystals, carbon dots and magnetic nanoparticles. The photonic bandgap of the composite films is modulated via interfacial interactions between the building blocks, and more efficiently via external magnetic field which can further enhance the selective reflection of the films with a maximum CPL anisotropic factor as high as -0.92, indicating the optimized condition for achieving CPL signals is basically when the photonic bandgap (PBG) are close to the emission peaks of nanocomposite films, which may essentially facilitate the selective reflection effect and leads to the output of opposite CPL signals. Such strategy would inevitably boost the development of carbon dots based chiral devices and reagents into the realm of chirality-related biological issues and next generation chiral optoelectronics.

Influence of buffer on colloidal stability, microstructure, and rheology of cellulose nanocrystals in hyaluronic acid suspensions.

Hyaluronic acid (HA) is a natural biopolymer found in various human tissues, while cellulose nanocrystals (CNCs) extracted from pulp fibers have unique rheological properties and biocompatibility. Due to the superior biomechanical properties of CNC and HA, a CNC-based HA suspension may be useful in biomedical applications. While buffers are an essential constituent of any suspension used for biomedical applications to maintain the desired pH level, they can significantly affect the properties of the suspension, including colloidal stability, microstructure, and rheological characteristics. To our knowledge, this is the first study analyzing the influence of buffer solutions on the suspension characteristics of HA/CNC systems, integrating both theoretical and experimental approaches. The results revealed an alignment between predictions of the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory and results from experiments characterizing a buffer-specific trend in colloidal stability. Suspensions with a higher energy barrier showed higher colloidal stability, with a lower tendency for phase separation and agglomerate formations. The microstructural analysis of CNC tactoids in the suspension revealed the existence of the hedgehog defect when dispersed in different buffer solutions. The defect is predicted to be caused by the pH-dependent protonation and deprotonation of HA. Furthermore, steady shear viscometry showed a microstructural-dependent shear viscosity trend, which, in turn, depends on the buffer solution. The study provides novel insights into the microstructural and bulk properties of HA and CNC suspensions in various buffer solutions. The results highlight the importance of solvent choice in tailoring the properties of the suspension for specific biomedical applications. These findings may be helpful in formulating HA and CNC suspensions for different biomedical applications, including drug delivery systems and viscosupplement injections.

Exploration of Unconventional excitation wavelength and dynamic emission in rare-earth doped multilayer core-shell Structures: Application for optical "Hard" and "Soft" switching.

Optical switches are increasingly acknowledged for their potential advantages over mechanical counterparts in various domains. However, research on optical switches remains relatively nascent, primarily focusing on applications like anti-counterfeiting, switching chemical reactions, etc., while neglecting the control of photocurrent switching. Here, we have developed NaYF4:30 %Er-NaYF4-NaYF4:20 %Ho-NaYF4 core-shell nanocrystals with unique upconversion (UC) multi-color emission properties under 1530 nm, 980 nm and 1150 nm laser excitations. These nanocrystals allow for optical control of circuit switching by modulating photocurrent signals in photosensitive circuits. The UC emission is due to the self-sensitization of rare earth ions in the core and shell. By adjusting the intermediate shell thickness, we have optimized the luminescence and investigated the mechanism. Combining these nanocrystals with a WO3 quantum dots (QDs) photochromic hydrogel, dynamic variation of UC emissions could be realized. Moreover, by combining with a commercial silicon photodetector, we constructed a photosensitive circuit demonstrating the modulation of photocurrent signal output and realized the "hard switching" of rapid circuit cutoff. Furthermore, by using the photochromic effect of WO3 QDs, the "soft switching" of slow circuit cutoff and recovery were also achieved. This work has significant implications for the development and application such as energy management system and smart home of optical switches in various fields.

Reaction-controlled shape evolution and insights into the growth mechanism of CsPbBr3 nanocrystals.

The correlation between structural transformation and optical characteristics of cesium lead bromide (CsPbBr3) nanocrystals (NCs) suggests insights into their growth mechanism and optical performance. Systematic control of reaction parameters led to the successful fabrication of on-demand shape-morphing CsPbBr3 NCs. Transmission electron microscopy observations showed that the shape transformation from nanocubes to microcrystals could be accelerated by increasing the precursor:ligand molar ratio and reaction time. Further evidence for orthorhombic CsPbBr3 NCs was obtained from their selected-area electron diffraction pattern, which exhibits a twin domain induced by the presence of large NCs. Likewise, we observed a substantial decrease in photoluminescence (PL) intensity of CsPbBr3 due to surface decomposition or surface ligand loss resulting from increased size. In addition, fusion of smaller particles having other dimensionality induced the increase in the PL full-width at half maximum. In particular, existence of larger bulk material caused a reduction in the peak intensity in the absorption spectra and a trend of decreasing tendency in intensity of the absorption bands related to bromoplumbate species provided direct evidence of fully converted Cs-oleate.

Construction of trace nitric oxide sensors at low temperature based on bulk embedded BiVO4 in SnO2 nanofibers with nano-heterointerfaces.

Constructing heterostructures is an effective way to improve the carrier mobility for metal oxide sensing material, since heterojunctions are usually built only on the surface of the material, the carrier transport efficiency inside the material still needs to be improved. In this paper, BiVO4 nanocrystals (BVO NCs) with an average size of 1 nm generated by pulsed laser irradiation were embedded in situ at the particle boundaries (PBs) of SnO2 nanofibers to form an effective n-n heterojunctions inside the material. After embedding the BVO NCs in the SnO2 samples, the response value for 10 ppm NO was improved to 48.91, which was 2.5 times higher than that of pure SnO2 at near room temperature (50 °C). Meanwhile, the detection limit was lowered to 50 ppb with excellent long term stability. Detailed analysis and theoretical calculations demonstrated that the formation of abundant n-n heterojunctions not only promotes the electron-hole separation and the carrier mobility, but also reduces the conductivity and adsorption energy of the material, which significantly improves its sensing performance. This work demonstrates a new approach to modulate the gas-sensing performance of metal oxide semiconductors by generating heterostructure inside the bulk of the material.

Structural, morphological, compositional, thermal, pasting, and functional properties of isolated Achira (Canna indica L.) starch: Review.

The aim of this study was to analyze the physicochemical properties of native Colombian Achira starch (Canna indica L.). Achira starch, with an amylose content of 49.07 % is classified as high amylose starch. Scanning electron microscopy (SEM) revealed grains with an average size of 54.34 µm in length and 34.93 µm in width, with spherical, ellipsoidal, and ovoid shapes. Mineral analysis identified phosphorus (P) and potassium (K) as the most important elements. For the first time, transmission electron microscopy (TEM) and X-ray diffraction (XRD) confirmed the presence of nanocrystals with a length of 23.95 nm, a width of 6.44 nm, and a hexagonal crystal structure (B-type starch). Thermogravimetric analysis (TGA) showed mass losses associated with water, lipids, and protein carbohydrates. Differential scanning calorimetry (DSC) showed gelatinization at 61.17 °C. The pasting profile indicated hydrogel behavior with a high peak viscosity of 13,690 cP due to the amylose content. The water absorption index (WAI) was 2.07 g/g, the water solubility index (WSI) was 3.04 g/g, and swelling power (SP) was 2.19 g/g. The presence of nanocrystals and the high amylose content indicate potential in the food industry.

Formulation and optimization of transferrin-modified genistein nanocrystals: In vitro anti-cancer assessment and pharmacokinetic evaluation.

In this research work, nanocrystals (NC) of poorly water-soluble drug genistein (Gen) were formulated to improve its aqueous solubility and bioavailability. Genistein nanocrystals (Gen-NC) were prepared by wet ball milling. The formulation was optimized using Box Behnken Design Expert to evaluate the impact of stabilizer concentration, drug concentration and quantity of zirconium beads (milling media) on NC size, polydispersity and zeta potential. The NCs were surface-decorated with transferrin (Tf) to form Tf modified Gen-NCs (Tf-Gen-NC) for improving cancer cell selectivity and cytotoxicity. The NC formulations were characterized by dynamic light scattering (DLS), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, X-ray power diffraction (XRD) and differential scanning calorimetry (DSC). The particle size distribution of the optimized formulation varied from 200 to 300 nm with poly dispersibility index (PDI) between 0.1 and 0.3. Tf-Gen-NC and Gen-NC released 96 % and 80 % of the drug content in 20 min at 37 °C, respectively, whereas only 18 % were released with the unprocessed drug. In vitro cytotoxicity was tested in pulmonary adenocarcinoma epithelial cells (A549) and fibroblast cell line (L929). The Tf-Gen-NC presented an enhanced anticancer effect. In vivo pharmacokinetic studies in mice after intraperitoneal administration showed that the Cmax of NC formulations were 2.5-fold higher compared to free Gen. The area under the curve from time of administration to 24 h was 2.5 to 3-fold higher when compared with unprocessed drug. This study shows the interest of Gen-NC in the development of new formulations for Gen as an anticancer drug.

Observation of Three-Photon Cascaded Emission from Triexcitons in Giant CsPbBr3 Quantum Dots at Room Temperature.

Colloidal semiconductor nanocrystals have long been considered a promising source of time-correlated and entangled photons via the cascaded emission of multiexcitonic states. The spectroscopy of such cascaded emission, however, is hindered by efficient nonradiative Auger-Meitner decay, rendering multiexcitonic states nonemissive. Here we present room-temperature heralded spectroscopy of three-photon cascades from triexcitons in giant CsPbBr3 nanocrystals. We show that this system exhibits second- and third-order correlation function values, g(2)(0) and g(3)(0,0), close to unity, identifying very weak binding of both biexcitons and triexcitons. Combining fluorescence lifetime analysis, photon statistics, and spectroscopy, we can readily identify emission from higher multiexcitonic states. We use this to verify emission from a single emitter despite high emission quantum yields of multiply excited states and comparable emission lifetimes of singly and multiply excited states. Finally, we present potential pathways toward control of the photon number statistics of multiexcitonic emission cascades.

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.

Functionalization of cellulose nanocrystals with a potent antimalarial compound: Synthesis, characterization, and biological studies.

Cellulosic materials, such as cellulose nanocrystals (CNCs), are biocompatible, biodegradable and have unique and fascinating biomedical applications. Calxinin (CXN), a potent multistage antimalarial compound was functionalised with CNCs to improve biocompatibility and enhance the bioactivity of the resulting CNC-CXN nano-conjugate. Elemental analysis, powder X-ray, SEM, AFM, Infrared, and solid-state NMR spectroscopic techniques confirmed the composition of novel CNC-CXN nano-conjugate. Next, CNC-CXN nano-conjugate did not exhibit apparent cytotoxic effects on the sensitive Vero E6 cell line up to a concentration of 4.66 µg/µl. The CNC-CXN nano-conjugate was also evaluated for its preliminary efficacy on Plasmodium falciparum (3D7) malaria parasite and showed a 50 % inhibitory concentration value of 0.02 µg/µl. Overall, the selectivity index (SI) of the CNC-CXN nano-conjugate significantly improved to 233, indicating its suitability for further validation studies in animal models.

Biorenewable Exfoliation of Electronic-Grade Printable Graphene Using Carboxylated Cellulose Nanocrystals.

The absence of scalable and environmentally sustainable methods for producing electronic-grade graphene nanoplatelets remains a barrier to the industrial-scale application of graphene in printed electronics and conductive composites. To address this unmet need, here we report the utilization of carboxylated cellulose nanocrystals (CNCs) extracted from the perennial tall grass Miscanthus × giganteus as a biorenewable dispersant for the aqueous liquid-phase exfoliation of few-layer graphene nanoplatelets. This CNC-based exfoliation procedure was optimized using a Bayesian machine learning model, resulting in a significant graphite-to-graphene conversion yield of 13.4% and a percolating graphene thin-film electrical conductivity of 3.4 × 104 S m-1. The as-exfoliated graphene dispersions were directly formulated into an aerosol jet printing ink using cellulose-based additives to achieve high-resolution printing (∼20 µm line width). Life cycle assessment of this CNC-based exfoliation method showed substantial improvements for fossil fuel consumption, greenhouse gas emissions, and water consumption compared to incumbent liquid-phase exfoliation methods for electronic-grade graphene nanoplatelets. Mechanistically, potential mean force calculations from molecular dynamics simulations reveal that the high exfoliation yield can be traced back to the favorable surface interactions between CNCs and graphene. Ultimately, the use of biorenewable CNCs for liquid-phase exfoliation will accelerate the scalable and eco-friendly manufacturing of graphene for electronically conductive applications.

Transforming Nanocrystals into Superhard Boron Carbide Nanostructures.

Boron carbide (B4+δC) possesses a large potential as a structural material owing to its lightness, refractory character, and outstanding mechanical properties. However, its large-scale industrialization is set back by its tendency to amorphize when subjected to an external stress. In the present work, we design a path toward nanostructured boron carbide with greatly enhanced hardness and resistance to amorphization. The reaction pathway consists of triggering an isomorphic transformation of covalent nanocrystals of Na1-xB5-xC1+x (x = 0.18) produced in molten salts. The resulting 10 nm B4.1C nanocrystals exhibit a 4-fold decrease of size compared to previous works. Solid-state 11B and 13C NMR coupled to density functional theory (DFT) reveal that the boron carbide nanocrystals are made of a complex mixture of atomic configurations, which are located at the covalent structural chains between B11C icosahedral building units. These nanocrystals are combined with a spark plasma-sintering-derived method operated at high pressure. This yields full densification while maintaining the particle size. The nanoscaled grains and high density of grain boundaries provide the resulting nanostructured bodies with significantly enhanced hardness and resistance to amorphization, thus delivering a superhard material.

A novel approach of differentiation of adenoma and carcinoma in lung cancer based on biogenic in situ synthesis of gold nanostructures on various oligonucleotide motifs.

A unique approach is introduced for constructing gold nanocrystals (AuNCs) with RNA motif-directed morphologies in a sequence-independent manner and its applications in the clinical area are described. By using this method, a label-free LSPR-based detection method for the SOX2OT transcript, long non-coding RNAs (lncRNAs), which is a prognostic indicator of poor survival in lung cancer patients is presented. For the first time, we examined how the structural changes of RNA after the heteroduplex formation with a specific DNA probe can change the morphology and LSPR band of AuNCs. Using this method, is was possible to differentiate lung squamous cell carcinoma from adenocarcinoma samples without a need for a prior amplification of the target lncRNA. The approach of using specific DNA probe enables the in situ synthesis of nanocrystals in a different way and expands this method for future translational medicine, particularly detection of specific RNA.

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.

Avocado Seed Starch-Based Films Reinforced with Starch Nanocrystals.

Biopolymers derived from biomass can provide the advantages of both biodegradability and functional qualities from a circular economy point of view, where waste is transformed into raw material. In particular, avocado seeds can be considered an interesting residue for biobased packaging applications due to their high starch content. In this work, avocado seed starch (ASS)-based films containing different glycerol concentrations were prepared by solvent casting. Films were also reinforced with starch nanocrystals (SNCs) obtained through the acid hydrolysis of ASS. The characterization of the extracted starch and starch nanocrystals by scanning electron microscopy, X-ray diffraction, and thermogravimetric analysis has been reported. Adding 1% of SNCs increased elastic modulus by 112% and decreased water vapor permeability by 30% with respect to neat matrix. Interestingly, the bioactive compounds from the avocado seed provided the films with high antioxidant capacity. Moreover, considering the long time required for traditional plastic packaging to degrade, all of the ASS-based films disintegrated within 48 h under lab-scale composting conditions. The results of this work support the valorization of food waste byproducts and the development of reinforced biodegradable materials for potential use as active food packaging.

Effect of salt ions (Na+, Ca2+ and Mg2+) and EOR anionic and nonionic surfactants on the dispersion stability of cellulose nanocrystals.

The application of cellulose nanocrystals (CNCs) in enhanced oil recovery (EOR) is a developing hotspot. To improve the stability of CNCs in salt environments, the effects of sodium dodecylbenzene sulfonate (SDBS) and polyoxyethylene sorbitan monooleate (Tween 80) on the stability of CNCs in the presence of sodium (Na+), calcium (Ca2+) and magnesium (Mg2+) were investigated. The range of salt ions and the stability mechanism for improving the CNCs stability in the presence of SDBS and Tween 80 were pointed out. SDBS improved the stability of CNCs in the presence of 30-100 mM Na+, 1-2 mM Ca2+ and 2 mM Mg2+, respectively. Tween 80 improved the stability of CNCs in the presence of Na+ ≤ 300 mM, Ca2+ ≤ 10 mM and Mg2+ ≤ 10 mM, respectively. The mechanism was explained by the bridging effect of salt ions, electrostatic effect and spatial stability effect. The combined systems of surfactants (SDBS and Tween 80) with CNCs exhibited strong emulsifying properties, low interfacial tension (0.023 mN/m and 1.85 mN/m), and the ability to alter the wettability of oil wet rocks. This made the combined systems have better oil displacement performance.

NIR-II Anti-Stokes Luminescence Nanocrystals with 1710 nm Excitation for in vivo Bioimaging.

Anti-Stokes luminescence (ASL) based on lanthanide nanocrystals holds immense promise for in vivo optical imaging and bio-detection, which benefits from filtered autofluorescence. However, the current longest emission and excitation wavelengths of lanthanide ASL system were shorter than 1200 nm and 1532 nm, respectively, which limited tissue penetration depth and caused low signal-to-noise ratio (SNR) of in vivo imaging due to tissue scattering and water absorption. In this work, we extended the excitation wavelength to 1710 nm with the second near-infrared (NIR-II, 1000-1700 nm) emission up to 1650 nm through a novel ASL nanocrystal LiYF4:10%Tm@LiYF4:70%Er@LiYF4. Compared with 1532 nm excited ASL nanoprobes, the 1710 nm excited nanocrystals could improve in vivo imaging SNR by 12.72 folds. Based on this excellent imaging performance of the proposed ASL nanoprobes, three-channel in vivo dynamic multiplexed imaging was achieved, which quantitatively revealed metabolic rates of intestinal dynamics and liver enrichment under anesthetized and awake states. This innovative ASL nanoprobes and dynamic multiplexed imaging technology would be conducive to optimizing dosing regimen and treatment plans across various physiological conditions.

Tragacanth gum hydrogels with cellulose nanocrystals: A study on optimizing properties and printability.

This study investigates a novel all-polysaccharide hydrogel composed of tragacanth gum (TG) and cellulose nanocrystals (CNCs), eliminating the need for toxic crosslinkers. Designed for potential tissue engineering applications, these hydrogels were fabricated using 3D printing and freeze-drying techniques to create scaffolds with interconnected macropores, facilitating nutrient transport. SEM images revealed that the hydrogels contained macropores with a diameter of 100-115 µm. Notably, increasing the CNC content within the TG matrix (30-50 %) resulted in a decrease in porosity from 83 % to 76 %, attributed to enhanced polymer-nanocrystal interactions that produced denser networks. Despite the reduced porosity, the hydrogels demonstrated high swelling ratios (890-1090 %) due to the high water binding capacity of the hydrogel. Mechanical testing showed that higher CNC concentrations significantly improved compressive strength (27.7-49.5 kPa) and toughness (362-707 kJ/m3), highlighting the enhanced mechanical properties of the hydrogels. Thermal analysis confirmed stability up to 400 °C and verified ionic crosslinking with CaCl2. Additionally, hemolysis tests indicated minimal hemolytic activity, affirming the biocompatibility of the TG/CNC hydrogels. These findings highlight the potential of these hydrogels as advanced materials for 3D-printed scaffolds and injectable hydrogels, offering customizable porosity, superior mechanical strength, thermal stability, and biocompatibility.

In Situ Driven Formation of Anatase/Brookite/Rutile Heterojunction N/TiO2 Nanocrystals as Sustainable Visible-Light Catalysts.

Visible-light active anatase/brookite/rutile (A/B/R) ternary N-doped titania (N/TiO2) crystals are successfully prepared by a facile sol-gel method using titanium butoxide and benign N-dopant source, guanidinium chloride. Systematically varying the aging time (1, 4, 8, and 12 d), its influence on physicochemical properties of as-obtained spherical heterojunction nanomaterials is studied. Detailed characterizations confirm that a substantial amount of anatase (88% to 50%) is transformed to rutile (2% to 38%) via intermediate brookite phase (9% to 25%) as the function of aging time; not only the A/B/R phase content of the samples is tuned by sol-gel aging time of the precursors solution but also their optical-response and methylene blue photocatalytic properties are profoundly dictated. Notably under visible-light irradiation, the photostable rutile rich mesoporous A/B/R triphasic N/TiO2 (50% A, 12% B, 38% R) aged for 12 d demonstrates higher degradation activity (97%) with a faster degradation rate (0.033 min-1) than both lesser aged N/TiO2 and undoped titania. This enhancement is attributed to the synergistic effect of interstitial-N-doping and optimal A/B/R interfacial charge transfer that leads to higher light absorption, lower bandgap energy and well-separated charge carriers. The current work provides a new perspective for designing highly active visible-light heterostructure nanomaterials with controllable phase composition.

Large-scale heterogeneous synthesis of monodisperse high performance colloidal CsPbBr3 nanocrystals.

Colloidal lead halide perovskite nanocrystals (LHP NCs) are promising semiconductor materials for optoelectronic devices, but the high ionicity of LHP NCs makes their crystallization control and post-treatment difficult. Here, phosphonic acids (PAs) are employed as ligands to design a solid-liquid heterogeneous reaction system to regulate the LHP NC crystallization and achieve the desired focusing growth. During the heterogeneous synthesis, the precursors in the liquid phase are responsible for the burst nucleation and initial growth of NCs. Afterwards, the focusing growth of NCs is supported by the precursors released from the solid phase. In addition, the strong binding ability of PAs enables effective passivation of LHP NCs. Without post-treatment, gram-scale monodisperse CsPbBr3 NCs having photoluminescence with a full width at half-maximum of 18 nm and a quantum yield of near-unity are obtained. The CsPbBr3 NCs covered by a compact ligand layer keep initial quantum yield even after 18 cycles of purification, exhibiting excellent stability against polar solvents, ultraviolet irradiation and heat treatment. As scintillators, the prepared CsPbBr3 NCs show strong radioluminescence emission and high-resolution X-ray imaging.