Nanocrystal Films Research Articles

Precise Control Light Emission of PVDF-CH3NH3PbBr3-xClx Nanocrystalline Films Using a Cl-(CH3OH)n System.

Methylammonium lead halide perovskites with highly efficient pure-color or white-light generation have gained increasing scientific interest and promote the development of a great commercial opportunity in displays, lighting, and other applications. However, the poor stabilities, lead toxicity, and unfriendly solvents and ligands in the growth process severely restrict their commercial application. Here, we proposed a green method for preparing uniform and stable polymer-encapsulated photoluminescence (PL) tunable CH3NH3PbBr3-xClx NC thin films at room temperature. Utilizing the swelling effect between alcohol compounds and organic polymers and the ionization of NaCl in methanol solution, the anion exchange process can be achieved rapidly within 7 min. Moreover, the PL wavelengths of the CH3NH3PbBr3-xClx NCs films were precisely tuned with steps as fine as 2 nm. Experimental results showed that NaCl dissolved in methanol solution can form Cl-(CH3OH)n, which brings ionized Cl into the polymer-encapsulated CH3NH3PbBr3 NCs film for CH3NH3PbBr3-xClx NCs film growth. Based on the swelling and anion exchange dynamics, a modified NaCl-CH3OH-MABr solution system was developed to trigger CH3NH3PbBr3-xClx NCs film PL emission tuning from 528 to 463 nm with several-fold intensity enhancement. The realization of precisely controlled photoluminescence from the perovskite nanocrystal film would have wide applications in the optical and imaging fields.

Chitosan–Chitin Nanocrystal Films from Lobster and Spider Crab: Properties and Environmental Sustainability

Chitosan–Chitin Nanocrystal Films from Lobster and Spider Crab: Properties and Environmental Sustainability

Probing the cw-Laser-Induced Fluorescence Enhancement in CsPbBr3 Nanocrystal Thin Films: An Interplay between Photo and Thermal Activation.

Perovskite nanocrystals hold significant promise for a wide range of applications, including solar cells, LEDs, photocatalysts, humidity and temperature sensors, memory devices, and low-cost photodetectors. Such technological potential stems from their exceptional quantum efficiency and charge carrier conduction capability. Nevertheless, the underlying mechanisms of photoexcitation, such as phase segregation, annealing, and ionic diffusion, remain insufficiently understood. In this context, we harnessed hyperspectral fluorescence microspectroscopy to advance our comprehension of fluorescence enhancement triggered by UV continuous-wave (cw) laser irradiation of CsPbBr3 colloidal nanocrystal thin films. Initially, we explored the kinetics of fluorescence enhancement and observed that its efficiency (φph) correlates with the laser power (P), following the relationship φph = 7.7⟨P⟩0.47±0.02. Subsequently, we estimated the local temperature induced by the laser, utilizing the finite-difference method framework, and calculated the activation energy (Ea) required for fluorescence enhancement to occur. Our findings revealed a very low activation energy, Ea ∼ 9 kJ/mol. Moreover, we mapped the fluorescence photoenhancement by spatial scanning and real-time static mode to determine its microscale length. Below a laser power of 60 μW, the photothermal diffusion length exhibited nearly constant values of approximately (22 ± 5) μm, while a significant increase was observed at higher laser power levels. These results were ascribed to the formation of nanocrystal superclusters within the film, which involves the interparticle spacing reduction, creating the so-called quantum dot solid configuration along with laser-induced annealing for higher laser powers.

Adjustable Multicolor Doped Cellulose Nanocrystal Film with Excitation and Temperature Dependence for All-Weather Anticounterfeiting in Sunlight and Darkness

Adjustable Multicolor Doped Cellulose Nanocrystal Film with Excitation and Temperature Dependence for All-Weather Anticounterfeiting in Sunlight and Darkness

High‐efficiency modification of PET by the low addition of a self‐assembled functional nanocellulose film prepared from waste paper

AbstractPolyethylene terephthalate (PET) is a conventional packaging material. Its modification has attracted immense attention in the industry and academia. Here, office waste paper, white cardboard waste, and waste corrugated paper were first employed as raw materials for cellulose nanocrystal (CNC) extraction by acid hydrolysis. Thereafter, CNC/PET composite films with various CNC additions were prepared via a self‐assembly technique. The results revealed that the CNCs formed a self‐assembled film on the PET surface via the synergistic effect of the complex interactions among the CNCs as well as between the CNCs and PET. Moreover, the CNCs improved the barrier property of PET and decreased the oxygen and water vapor transmittances of CNC/PET by 30.7% and 21.7%, respectively. Additionally, the coating of the PET surface with 0.2 wt.% CNCs extracted from the waste paper decreased the surface wettability of PET, exhibiting application potentials in the hydrophobic modification of polymers. This study realized waste paper recycling and provided a basis for constructing self‐assembled functional films on PET surfaces. The findings and insights of this study could exhibit application potentials in the fields of waste recycling and packaging materials.Highlights A functional cellulose nanocrystal (CNC) film is prepared from waste paper. Self‐assembled CNC is coated on a PET surface to form a CNC/PET composite film. The synergistic interactions among CNCs and between CNC and PET modified PET. The low addition of CNCs realized the efficiency modification of PET. The study achieves waste paper recycling and high‐value utilization.

Microsecond-response perovskite light-emitting diodes for active-matrix displays

Perovskite light-emitting diodes (PeLEDs) could be of use in the development of active-matrix displays. However, due to ion migration in crystal structure, PeLEDs have electroluminescence rise times over milliseconds, which is problematic for the development of high-refresh-rate displays. Here, we show that the electroluminescence rise time of PeLEDs can be reduced to microseconds using an individual-particle passivation strategy. The approach is based on BF4− ions that can passivate every nanocrystal in a perovskite emissive layer during film deposition. It leads to a defect-free film with discrete nanostructure and excellent crystallinity, which inhibits ion migration. Our strategy can be applied in perovskite nanocrystal films with different colours: red (635 nm), green (520 nm) and blue (475 nm). These PeLEDs all demonstrate response times within microseconds and high external quantum efficiencies of 22.7%, 26.2% and 18.1%, respectively. This allows us to create microsecond-response active-matrix PeLEDs that exhibit external quantum efficiencies above 20% at a display brightness of 500–3,000 cd m−2 for green devices with a resolution of 30 pixels per inch. We also develop microsecond-response red, green and blue active-matrix displays with 90 pixels per inch.

Lysine-mediated surface modification of cellulose nanocrystal films for multi-channel anti-counterfeiting

Utilizing advanced multiple channels for information encryption offers a powerful strategy to achieve high-capacity and highly secure data protection. Cellulose nanocrystals (CNCs) offer a sustainable resource for developing information protection materials. In this study, we present an approach that is easy to implement and adapt for the covalent attachment of various fluorescence molecules onto the surface of CNCs using the Mannich reaction in aqueous-based medium. Through the use of the Mannich reaction-based surface modification technique, we successfully achieved multi-color fluorescence in the resulting CNCs. The resulting CNC derivatives were thoroughly characterized by two dimensional heteronuclear single quantum coherence nuclear magnetic resonance (2D HSQC NMR) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron (XPS) spectroscopy. Notably, the optical properties of CNCs were well maintained after modification, resulting in films exhibiting blue and red structural colors. This enables the engineering of highly programmable and securely encoded anti-counterfeit labels. Moreover, subsequent coating of the modified CNCs with MXene yielded a highly secure encrypted matrix, offering advanced security and encryption capabilities under ultraviolet, visible, and near-infrared wavelengths. This CNC surface-modification enables the development of multimodal security labels with potential applications across various practical scenarios.

Multifunctional ligand-manipulated luminescence and electric transport of CsPbI3 perovskite nanocrystals for red light-emitting diodes

Perovskite nanocrystal (NC) light-emitting diodes (LEDs) are promising for high-quality displays due to their excellent optoelectronic properties, but the highly labile surface and insulating long-chain capping ligands of NCs are the main constraint for improving device performance. Herein we developed a facile post-treatment for CsPbI3 NCs with 2-thiophenethylamine chloride (TEAC) to eliminate trap states and replace the native ligands on NCs, enabling manipulation of their luminescence and electrical properties. Hence, the modified CsPbI3 NCs exhibit a high photoluminescence quantum yield of 92.5 % even after the purification processes due to the comprehensive defect suppression of TEAC ligands originating from the synergistic effect of halogen compensation and coordination of S atom in the thiophene ring with Pb2+. Moreover, with the assistance of the highly conductive TEAC ligands, CsPbI3 NC films show significant improvement in carrier transport properties. Based on the elaborate surface reconstruction of CsPbI3 NCs, we achieve an external quantum efficiency of 17.3 % with a high operational lifetime of 9.8 h at an initial luminance of 100 cd m−2 for red perovskite LEDs (PeLEDs), which is a more than 2-fold improvement compared to the control NC-based device. We demonstrate that this high performance of the fabricated PeLEDs is attributed to the resurfacing chemistry of CsPbI3 NCs by the thiophene-based ligand passivation, simultaneously enabling the trap-defect elimination and efficient charge transport in the CsPbI3 NC film.

Structural, Optical, and Mechanical Insights into Cellulose Nanocrystal Chiral Nematic Film Engineering by Two Assembly Techniques.

Iridescent cellulose nanocrystal (CNC) films with chiral nematic nanostructures exhibit great potential in optical devices, sensors, painting, and anticounterfeiting applications. CNCs can assemble into a chiral nematic liquid crystal structure by evaporation-assisted self-assembly (EISA) and vacuum-assisted self-assembly (VASA) techniques. However, there is a lack of comprehensive examinations of their structure-property correlations, which are essential for fabricating materials with unique properties. In this work, we gained insights into the optical, mechanical, and structural differences of CNC films engineered using the two techniques. In contrast to the random self-assembly at the liquid-air interface in EISA, the continuous external pressure in the VASA process forces CNCs to assemble at the filter-liquid interface. This results in fewer defects in the interfaces between tactoids and highly ordered cholesteric phases. Owing to the distinct CNC assembly behaviors, the films prepared by these two methods show great differences in the nanostructure, microstructure, and macroscopic morphology. Consequently, the highly ordered cholesteric structure gives VASA-CNC films a more uniform structural color and enhanced mechanical performance. These fundamental understandings of the relationship of structure-property nanoengineering through various assembly techniques are essential for designing and constructing high-performance chiral iridescent CNC materials.

Blue Lead‐Free Perovskite Derivatives: Structural Diversity, Luminescence Properties and Light‐Emitting Diode Applications

AbstractHalide perovskite light‐emitting diodes (LEDs) have made remarkable advancements in both efficiency and stability. However, when compared to green and red LEDs, blue perovskite LEDs still lag behind in terms of efficiency and stability. Presently, efficient blue LEDs primarily rely on lead‐based perovskites, which goes against the environmentally friendly practices and restricts potential industrial applications. Consequently, there has been a surge of interest in academic research toward developing blue LEDs using lead‐free perovskites. This paper provides a comprehensive review of the structural diversity of lead‐free perovskite derivatives used for blue emission, encompassing Sn‐, Zr‐, Bi‐, Sb‐, Cu‐, Zn‐based halides as well as double perovskites. Various material synthesis techniques are discussed, such as nanocrystal preparation and film preparation. Additionally, the photoluminescence properties for different energy band structures are outlined, along with the luminescence mechanism involving energy transfer and strategies for enhancing luminous efficiency. The advancement in efficiency and stability of lead‐free perovskite LEDs is also examined in this review. Finally, the current challenges and future opportunities in advancing research on blue lead‐free perovskite derivatives and their potential application in LED technology is emphasized.

Application of pectin/cellulose nanocrystal films loaded with summer savory essential oil as a novel packaging for chicken breast fillets

Application of pectin/cellulose nanocrystal films loaded with summer savory essential oil as a novel packaging for chicken breast fillets

Spray pyrolysis–deposited NiO film as a hole-injection layer for CsPbBr3 nanocrystal-based light-emitting diodes

In perovskite-based light-emitting diodes (LEDs), employing an inorganic material for the hole-injection layer instead of an organic material is crucial for attaining optimal performance and device stability. This layer needs to exhibit [Formula: see text] -type conductivity with high carrier mobility while being fabricated with a simple and industrially compatible method. In this study, uniform and thin [Formula: see text] -type NiO films were deposited through spray pyrolysis in an air atmosphere. The as-deposited film showed poor crystallinity, and high resistance reduced hole-injection performance. Subsequent thermal treatment at 500∘C enhanced the crystallinity of the layer, reducing resistance and improving LED performance. The film exhibited [Formula: see text] -type semiconductor characteristics, and its carrier mobility, carrier concentration and resistivity were 53.0 × [Formula: see text]cm3, 116cm2⋅ [Formula: see text] and 0.98[Formula: see text] ⋅ [Formula: see text], respectively. Moreover, a compact [Formula: see text] nanocrystal (NC) film as an emitting layer was deposited with a centrifugal coating technique. The resulting LED component featuring a fluoride-doped tin oxide (FTO)/NiO/[Formula: see text] NCs/tris-(1-phenyl-1H-benzimidazole)/LiF/Au structure and demonstrating high luminance, current efficiency and external quantum efficiency (EQE) reached 12,000 cd⋅[Formula: see text], 8.8 cd ⋅ [Formula: see text] and 3.56%, respectively, at 5.5 V. Our work offers a simple and unique approach for accelerating the development of advanced interfacial materials and circumventing major interfacial problems in solution-processed perovskite NC films for high-performance LEDs.

Superfluorescence in Metal Halide Perovskites

AbstractSuperfluorescence (SF) is a unique quantum optical phenomenon where an ensemble of atoms or molecules exhibit coherent emission of an intense burst of light of high directionality, with temporal coherence. SF exhibits ultrafast optical characteristics and is considerably explored in diverse inorganic and hybrid semiconductor materials at cryogenic temperatures, including inorganic and hybrid metal halide perovskites. Notably, SF is reported in different perovskites’ nanocrystal superlattices, alongside two examples in thin films, impressively achieving SF at room temperature. The density of quantum emitters, excited state characteristics, interaction strengths, and temperature all affect the SF threshold. Although significant progress is reported in the observance of SF phenomena, a full interpretation of the relationship between the factors that determine the SF threshold and the intrinsic material properties remains unclear. This review addresses the current state‐of‐the‐art observations of SF in perovskite systems, such as nanocrystal superlattices and thin films, elucidating the optical properties, ultrafast dynamics, and the proposed mechanisms for room‐temperature SF. The review concludes with a discussion on the existing challenges, unresolved questions, and future perspectives for advancing perovskite SF research

Surface Modification of Cellulose Nanocrystal Films via RAFT Polymerization for Adsorption of PFAS

Cellulose nanocrystals (CNCs) are bio-based materials able to be functionalized following different approaches, which expands their range of applications. One such approach is surface-initiated polymerization, which involves the attachment of an initiator to the CNC’s surface to initiate the growth of the polymer. This work reports the modification of CNCs using the described approach. First, a CNC-based film was prepared, on which an initiator (RAFT agent) was grafted, and then (trimethylaminoethyl methacrylate, a positively charged monomer, was polymerized using reversible addition–fragmentation chain-transfer (RAFT) polymerization. The CNC film was successfully modified and fully characterized. Different degrees of polymerization were targeted to emphasize the effect of the positively charged polymer and their chain length on the adsorption efficiency. The results showed that by increasing the chain length of the grafted polymer, up to 80% of both pollutants could be removed, with a faster adsorption of PFOS as compared to PFOA.

Control of Lateral Assembly and Vertical Stacking in Spin-Coated Lead Halide Perovskite Nanocrystal Films for Enhanced Photoluminescence Efficiency

Control of Lateral Assembly and Vertical Stacking in Spin-Coated Lead Halide Perovskite Nanocrystal Films for Enhanced Photoluminescence Efficiency

Reversible Ligand Detachment from CdSe Quantum Dots Following Photoexcitation.

The nanocrystal-ligand boundaries of colloidal quantum dots (QDs) mediate charge and energy transfer processes that underpin photochemical and photocatalytic transformations at their surfaces. We used time-resolved infrared spectroscopy combined with transient electronic spectroscopy to probe vibrational modes of the carboxylate anchoring groups of stearate ligands attached to cadmium selenide (CdSe) QDs that were optically excited in solid nanocrystal films. The vibrational frequencies of surface-bonded carboxylate groups revealed their interactions with surface-localized holes in the excited states of the QDs. We also observed transient and reversible photoinduced ligand detachment from CdSe nanocrystals within their excited state lifetime. By probing both surface charge distributions and ligand dynamics on QDs in their excited states, we open a pathway to explore how the nanocrystal-ligand boundary can be understood and controlled for the design of QD architectures that most effectively drive charge transfer processes in solar energy harvesting and photoredox catalysis applications.

Synthesis, Structural Characterization and Temperature Effects on Chloroform Vapor Sensing Properties of ZnO Nanocrystals

In this study, nanocrystalline ZnO were synthesized onto glass substrates by using sol-gel method. Structural characterizations were performed by XRD, SEM and AFM techniques. Potential application of nanocrystal ZnO as chloroform sensor was investigated. Response of the fabricated thin films of the ZnO nanocrystals towards chloroform vapor was investigated depending on gas concentration (750-15000 ppm) between the temperatures of 22‒150 ºC in nitrogen ambient. Gas flow rates were controlled by using flow controller and flow meters. All the measurement system was computerized. XRD results revealed that thin film of the ZnO nanocrystals on the glass substrate was in crystal form and can be characterized by 036-1451 JCPDS number. Crystallite sizes of the ZnO nanocrystals were determined both by SEM images and the Scherrer equation. The crystallite sizes were calculated between 27.9 – 50.4 nm using the Scherrer equation. The sensors showed reversible response towards the chloroform vapor in the measured temperature and gas concentration range. Response time and sensitivity values of the sensors towards the chloroform vapor were also calculated. The increase in temperature caused to increase in sensitivity values. The best sensitivity values were obtained at 150 ºC.

Organosilicon-Based Ligand Design for High-Performance Perovskite Nanocrystal Films for Color Conversion and X-ray Imaging.

Perovskite nanocrystals (PNCs) bear a huge potential for widespread applications, such as color conversion, X-ray scintillators, and active laser media. However, the poor intrinsic stability and high susceptibility to environmental stimuli including moisture and oxygen have become bottlenecks of PNC materials for commercialization. Appropriate barrier material design can efficiently improve the stability of the PNCs. Particularly, the strategy for packaging PNCs in organosilicon matrixes can integrate the advantages of inorganic-oxide-based and polymer-based encapsulation routes. However, the inert long-carbon-chain ligands (e.g., oleic acid, oleylamine) used in the current ligand systems for silicon-based encapsulation are detrimental to the cross-linking of the organosilicon matrix, resulting in performance deficiencies in the nanocrystal films, such as low transparency and large surface roughness. Herein, we propose a dual-organosilicon ligand system consisting of (3-aminopropyl)triethoxysilane (APTES) and (3-aminopropyl)triethoxysilane with pentanedioic anhydride (APTES-PA), to replace the inert long-carbon-chain ligands for improving the performance of organosilicon-coated PNC films. As a result, strongly fluorescent PNC films prepared by a facile solution-casting method demonstrate high transparency and reduced surface roughness while maintaining high stability in various harsh environments. The optimized PNC films were eventually applied in an X-ray imaging system as scintillators, showing a high spatial resolution above 20 lp/mm. By designing this promising dual organosilicon ligand system for PNC films, our work highlights the crucial influence of the molecular structure of the capping ligands on the optical performance of the PNC film.

Comparative study of the near-infrared detection of PbSe fabricated using a sputter deposition method

Near-infrared (NIR) light is used in nondestructive spectroscopies to analyze various compounds in several applications. A PbSe nanocrystal film used in NIR detectors is fabricated using a magnetron sputtering process. The PbSe NIR detectors can be fabricated at a low cost and can operate at ambient temperatures. In this study, the surface morphology and chemical and crystal states of PbSe and its NIR detection performance are investigated and compared with existing reports in the literature. The PbSe film grown by sputtering exhibits nano- and columnar crystal structures, predominantly halite-like (100) face-centered cubic structures. The PbSe film contains PbO and SeO2 and exhibits dual-absorption band-to-band transitions at 0.43 and 0.52 eV. The sputtered PbSe film is used to fabricate an NIR photodetector with a metal-semiconductor-metal structure. The detector shows fast rise and decay times of 0.14 and 0.12 s, respectively, and responsivity of approximately 0.01 A/W under infrared illumination. Based on this study, a low-cost PbSe NIR detector that can operate at room temperature is developed for early fire detection.

Sodium-alginate-based indicator film containing a hydrophobic nanosilica layer for monitoring fish freshness

In this study, hydrophobic sodium alginate/anthocyanin/cellulose nanocrystal indicator films were fabricated by incorporating nanosilica (NS) as a waterproofing layer. The concentrations and formation methods (spraying (S), coating (C), and impregnation (I)) of the NS layer (denoted as NSS, NSC, NSI, respectively) were optimized. The results indicated that the optimum concentration of the NS layer was 5 % at a water contact angle (WCA) 110.5°. Further, Fourier transform infrared spectra showed the presence of SiOSi and SiCH3 groups in the NSS, NSC, and NSI films, and X-ray diffraction spectra indicated that original structures of these films were disordered. Moreover, the surface morphology, mechanical properties, and light transmission were affected by the NS layer, and the optimal layer was found to be NSI. After 10 days of storage at 100 % humidity, the NSI film exhibited low water vapor adsorption (37.22 g) and permeability (0.1484 g/m·s·Pa·10−11) and a high WCA (110.2°). In addition, the NSI film exhibited a visible color shift with an increasing pH of the buffer solution. A monitoring test of fish freshness showed that the NSI film displayed a distinctive color change corresponding to fish spoilage during 14 days of storage. This indicates that NSI has high potential in indicator film applications.