Synthesis and assembly of rare earth nanostructures directed by the principle of coordination chemistry in solution-based process

Synthesis under Normal Conditions and Morphology and Composition of AlF3 Nanowires

AlF3 has interesting electrophysical properties, due to which the material is promising for applications in supercapacitors, UV coatings with low refractive index, excimer laser mirrors, and photolithography. The formation of AlF3-based nano- and micro-wires can bring new functionalities to AlF3 material. AlF3 nanowires are used, for example, in functionally modified microprobes for a scanning probe microscope. In this work, we investigate the AlF3 samples obtained by the reaction of initial aluminum with an aqueous hydrofluoric acid solution of different concentrations. The peculiarity of our work is that the presented method for the synthesis of AlF3 and one-dimensional structures based on AlF3 is simple to perform and does not require any additional precursors or costs related to the additional source materials. All the samples were obtained under normal conditions. The morphology of the nanowire samples is studied using scanning electron microscopy. We performed an intermediate atomic force microscope analysis of dissolved Al samples to analyze the reactions occurring on the metal surface. The surface of the obtained samples was analyzed using a scanning electron microscope. During the analysis, it was found that under the given conditions, whiskers were synthesized. The scale of one-dimensional structures varies depending on the given parameters in the system. Quantitative energy-dispersive x-ray spectroscopy spectra are obtained and analyzed with respect to the feedstock and each other.

NIR-Triggered Generation of Reactive Oxygen Species and Photodynamic Therapy Based on Mesoporous Silica-Coated LiYF4 Upconverting Nanoparticles

To date, the increase in reactive oxygen species (ROS) production for effectual photodynamic therapy (PDT) treatment still remains challenging. In this study, a facile and effective approach is utilized to coat mesoporous silica (mSiO₂) shell on the ligand-free upconversion nanoparticles (UCNPs) based on the LiYF₄ host material. Two kinds of mesoporous silica-coated UCNPs (UCNP@mSiO₂) that display green emission (doped with Ho³⁺) and red emission (doped with Er³⁺), respectively, were successfully synthesized and well characterized. Three photosensitizers (PSs), merocyanine 540 (MC 540), rose bengal (RB), and chlorin e6 (Ce6), with the function of absorption of green or red emission, were selected and loaded into the mSiO₂ shell of both UCNP@mSiO₂ nanomaterials. A comprehensive study for the three UCNP@mSiO₂/PS donor/acceptor pairs was performed to investigate the efficacy of fluorescence resonance energy transfer (FRET), ROS generation, and in vitro PDT using a MCF-7 cell line. ROS generation detection showed that as compared to the oleate-capped and ligand-free UCNP/PS pairs, the UCNP@mSiO₂/PS nanocarrier system demonstrated more pronounced ROS generation due to the UCNP@mSiO₂ nanoparticles in close vicinity to PS molecules and a higher loading capacity of the photosensitizer. As a result, the three LiYF₄ UCNP@mSiO₂/PS nanoplatforms displayed more prominent therapeutic efficacies in PDT by using in vitro cytotoxicity tests.

Applications of rare earth oxides in catalytic ammonia synthesis and decomposition

Due to their unique structural and electronic properties, rare earth oxides have been widely applied as supports and promoters in catalytic ammonia synthesis and decomposition.

In vivo deep-tissue microscopy with UCNP/Janus-dendrimers as imaging probes: resolution at depth and feasibility of ratiometric sensing

Lanthanide-based upconverting nanoparticles (UCNPs) are known for their remarkable ability to convert near-infrared energy into higher energy light, offering an attractive platform for construction of biological imaging probes. Here we focus on in vivo high-resolution microscopy - an application for which the opportunity to carry out excitation at low photon fluxes in non-linear regime makes UCNPs stand out among all multiphoton probes. To create biocompatible nanoparticles we employed Janus-type dendrimers as surface ligands, featuring multiple carboxylates on one 'face' of the molecule, polyethylene glycol (PEG) residues on another and Eriochrome Cyanine R dye as the core. The UCNP/Janus-dendrimers showed outstanding performance as vascular markers, allowing for depth-resolved mapping of individual capillaries in the mouse brain down to a remarkable depth of ∼1000 μm under continuous wave (CW) excitation with powers not exceeding 20 mW. Using a posteriori deconvolution, high-resolution images could be obtained even at high scanning speeds in spite of the blurring caused by the long luminescence lifetimes of the lanthanide ions. Secondly, the new UCNP/dendrimers allowed us to evaluate the feasibility of quantitative analyte imaging in vivo using a popular ratiometric UCNP-to-ligand excitation energy transfer (EET) scheme. Our results show that the ratio of UCNP emission bands, which for quantitative sensing should respond selectively to the analyte of interest, is also strongly affected by optical heterogeneities of the medium. On the other hand, the luminescence decay times of UCNPs, which are independent of the medium properties, are modulated via EET only insignificantly. As such, quantitative analyte sensing in biological tissues with UCNP-based probes still remains a challenge.

Ultrathin 2D Rare-Earth Nanomaterials: Compositions, Syntheses, and Applications

Ultrathin 2D nanomaterials possess promising properties due to electron confinement within single or a few atom layers. As an emerging class of functional materials, ultrathin 2D rare-earth nanomaterials may incorporate the unique optical, magnetic, and catalytic behaviors of rare-earth elements into layers, exhibiting great potential in various applications such as optoelectronics, magnetic devices, transistors, high-efficiency catalysts, etc. Despite its importance, reviews on ultrathin 2D rare-earth nanomaterials or related topics are rare and only focus on a certain family of ultrathin 2D rare-earth nanomaterials. This work is the first comprehensive review in this impressive field, which covers all families of ultrathin 2D rare-earth nanomaterials, illustrating their compositions, syntheses, and applications. After summarizing the current achievements, the challenges and opportunities of future research on ultrathin 2D rare-earth nanomaterials are evaluated.

Highly efficient infrared to visible up-conversion emission tuning from red to white in Eu/Yb co-doped NaYF4 phosphor

Eu/Yb co-doped NaYF₄ phosphors have been synthesized by the combustion method. The Eu doping was fixed and the effect of Yb doping concentration on the structural, morphological and luminescence properties has been investigated. X-ray diffraction analysis revealed that the phosphors consisted of mixed α- and β-phases, but the β-phase was dominant. All elements of the host and dopants, as well as adventitious C, were detected using X-ray photoelectron spectroscopy. The surface morphology showed a microrod-like structure with sharp hexagonal edges. Energy dispersive X-ray spectroscopy spectra proved the formation of the desired materials. The photoluminescence spectra illustrated the optical emission properties of Eu³⁺ in the red region when excited at 394 nm, while, under the same excitation, Yb³⁺ ions gave emission at 980 nm. The up-conversion (UC) emission of Eu/Yb co-doped NaYF₄ produced a white color at the higher concentration of Yb excited by a 980 nm laser, which was made possible by green emission of Er contamination (from Yb source) and blue emission of Eu²⁺ ions. The lifetime of the Eu³⁺ UC luminescence at 615 nm was also affected by the Yb doping concentration. The temperature sensitivity associated with the Er³⁺ peaks at 520 and 542 nm was assessed as a function of temperature and the maximum of 0.0040 K^-1 occurred at 463 K.

Rare earth double perovskites: a fertile soil in the field of perovskite oxides

This review summarizes the compositions, syntheses, and applications of rare earth A₂B′B′′O₆ double perovskites.

Fluorolytic Sol–Gel Synthesis of Nanometal Fluorides: Accessing New Materials for Optical Applications

The potential of fluorolytic sol–gel synthesis for a wide variety of applications in the field of optical materials is reviewed. Based on the fluorolytic sol–gel synthesis of nanometal fluorides, sols of complex fluorometalates have become available that exhibit superior optical properties over known classical binary metal fluorides as, for instance, magnesium fluoride, calcium fluoride, or strontium fluoride, respectively. The synthesis of transparent sols of magnesium fluoroaluminates of the general composition MgxAlFy, and fluoroperovskites, [K1−xNax]MgF3, is reported. Antireflective coatings fabricated from MgF2, CaF2, MgxAlFy, and [K1−xNax]MgF3 sols and their relevant properties are comprehensively described. Especially the heavier alkaline earth metal fluorides and the fluorperovskites crystallizing in a cubic crystal structure are excellent hosts for rare earth (RE) metals. Thus, the second chapter reflects the synthesis approach and the properties of luminescent systems based on RE-doped alkaline earth metal fluorides and [K1−xNax]MgF3 phases.

Lanthanide-Coordinated Black Phosphorus

Black phosphorus (BP) possesses unique physical properties and, owing to its intrinsic instability, the proper surface and chemical coordination is the key point in many applications. Herein, a facile and efficient surface lanthanide-coordination strategy based on lanthanide (Ln) sulfonate complexes is designed to passivate and functionalize different BP-based nanostructures including quantum dots, nanosheets, and microflakes. By means of Ln-P coordination, the lone-pair electrons of phosphorus are occupied, thus preventing oxidation of BP, and the LnL3 @BP exhibits excellent stability in both air and water. Furthermore, accompanied by the original photothermal performance of BP nanostructures, the Gd-coordinated BP has high R1 relativities in magnetic resonance (MR) imaging, and other Ln (Tb, Eu, and Nd) coordinated BP structures exhibit fluorescence spanning the visible to near-infrared regions. Not only is LnL3 surface passivation an efficient method to enhance the stability of BP, but also the MR or fluorescence derived from lanthanide ions extends the application of BP to optoelectronics and biomedical engineering.

Highly Photostable Near-IR-Excitation Upconversion Nanocapsules Based on Triplet-Triplet Annihilation for in Vivo Bioimaging Application

Triplet-triplet-annihilation-based upconversion (TTA-UC) imaging boasts a low-excitation irradiance and an uncanny lack of autofluorescence interference. Because of these promising features, this approach has been the subject of intensifying investigation. Despite the ideal features, the classical approach of TTA-UC imaging suffers from some crucial drawbacks. A major deficiency of the system lies within its poor photostability, especially for a near-IR-excitation system. Here we report a reduction strategy to improve the TTA-UC photostability. The poor photostability of TTA-UC can be attributed to singlet oxygen generation by the sensitizer under irradiation. We control the singlet oxygen by including a reductive solvent, which consumes the singlet oxygen, thereby improving the TTA-UC photostability. We also prepared TTA-UC nanocapsules with reductive solvent soybean oil inside. In comparison to nonreductive solvents such as toluene, our system shows a significant enhancement to the TTA-UC photostability. The prepared TTA-UC nanocapsules were then used for whole-animal deep imaging with a high signal-to-noise ratio.

Lanthanide ions-induced formation of hierarchical and transparent polysaccharide hybrid films

Nacre-like hybrid films based on N-succinyl chitosan (NSC), sodium alginate (SA) and lanthanide ions were fabricated via coordination interactions. In this work, the binary building blocks (NSC and SA) were self-assembled into aligned hydrogel films by coordination with lanthanide ions, and hierarchical NSC-SA hybrid films were obtained upon drying. Two species of lanthanide ions (Gd³⁺ and Yb³⁺) were used to fabricate the hierarchical NSC-SA hybrid films. The as-prepared NSC-SA hybrid films exhibit high tensile strength and stability. The tensile strength and toughness of as-prepared hybrid films reach 122.10MPa and 3.89MJm^-3, respectively. Meanwhile, the well-aligned lamellar microstructures also exhibit a good light transmittance. The highest light transmittance reaches 92% for NSC-SA hybrid films at 760nm. This fabrication method for hierarchical NSC-SA hybrid films is innovative due to the utilization of rare earth coordination bonding, and can serve as the basic strategy for the construction of high-performance composites in the near future.

Nile Red Derivative-Modified Nanostructure for Upconversion Luminescence Sensing and Intracellular Detection of Fe(3+) and MR Imaging

Iron ion (Fe(3+)) which is the physiologically most abundant and versatile transition metal in biological systems, has been closely related to many certain cancers, metabolism, and dysfunction of organs, such as the liver, heart, and pancreas. In this Research Article, a novel Nile red derivative (NRD) fluorescent probe was synthesized and, in conjunction with polymer-modified core-shell upconversion nanoparticles (UCNPs), demonstrated in the detection of Fe(3+) ion with high sensitivity and selectivity. The core-shell UCNPs were surface modified using a synthesized PEGylated amphiphilic polymer (C18PMH-mPEG), and the resulting mPEG modified core-shell UCNPs (mPEG-UCNPs) show good water solubility. The overall Fe(3+)-responsive upconversion luminescence nanostructure was fabricated by linking the NRD to the mPEG-UCNPs, denoted as mPEG-UCNPs-NRD. In the nanostructure, the core-shell UCNPs, NaYF4:Yb,Er,Tm@NaGdF4, serve as the energy donor while the Fe(3+)-responsive NRD as the energy acceptor, which leads to efficient luminescence resonance energy transfer (LRET). The mPEG-UCNPs-NRD nanostructure shows high selectivity and sensitivity for detecting Fe(3+) in water. In addition, benefited from the good biocompatibility, the nanostructure was successfully applied for detecting Fe(3+) in living cells based on upconversion luminescence (UCL) from the UCNPs. Furthermore, the doped Gd(3+) ion in the UCNPs endows the mPEG-UCNPs-NRD nanostructure with effective T1 signal enhancement, making it a potential magnetic resonance imaging (MRI) contrast agent. This work demonstrates a simple yet powerful strategy to combine metal ion sensing with multimodal bioimaging based on upconversion luminescence for biomedical applications.

Upconversion nanoparticle arrays for detecting glycated hemoglobin with high sensitivity and good reusability

Lanthanide-doped upconversion nanoparticles (UCNPs) have attracted extensive interest in bio-applications due to their unique optical properties by converting near infrared excitation to visible emission.

Hierarchical alginate biopolymer papers produced via lanthanide ion coordination

A layered alginate-based biopolymer paper with a hierarchical structure and excellent mechanical properties was prepared via lanthanide ions coordination.

Sodium citrate (Na3Cit)-assisted hydrothermal synthesis and characterization of twinned hemisphere shaped La2(MoO4)3:Eu3+ phosphors

Sodium citrate (Na₃Cit) mediated hydrothermal synthesis and characterization of twinned hemisphere shaped La₂(MoO₄)₃:Eu³⁺ phosphors.

Chainlike assembly of oleic acid-capped NaYF4:Yb,Er nanoparticles and their fixing by silica encapsulation

We demonstrate, through simply tuning the polarity of the dispersant system, oleic acid-capped NaYF₄ nanoparticles can be self-assembled into chainlike structures, which were further fixed by silica encapsulation via the Stöber method.

One-step hydrothermal synthesis of Sc2Mo3O12:Ln3+ (Ln = Eu, Tb, Dy, Tb/Eu, Dy/Eu) nanosheets and their multicolor tunable luminescence

The energy transfer of MoO₄²⁻ → Tb³⁺ (Dy³⁺) → Eu³⁺ and multicolor tunable emission occurred in Sc₂Mo₃O₁₂ nanosheets prepared by one-step hydrothermal synthesis.

Facile hydrothermal synthesis of Tb2(MoO4)3:Eu3+ phosphors: controllable microstructures, tunable emission colors, and the energy transfer mechanism

Microsphere-like Tb₂(MoO₄)₃ structures have been successfully synthesized by a facile hydrothermal method with the subsequent calcination treatment.

Regiospecific Hetero-Assembly of DNA-Functionalized Plasmonic Upconversion Superstructures

We report a novel strategy for regiospecific hetero-assembly of DNA-modified gold nanoparticles (DNA-AuNPs) onto upconversion nanoparticles (UCNPs) into hybrid lab-on-a-particle systems. The DNA-AuNPs have been assembled onto the hexagonal plate-like UCNPs with well-regulated stoichiometry and controlled organization onto the different facets of UCNP, forming various addressable superstructures. The fine-tuning of stoichiometry and organization is realized by biorecognition specificity of DNA toward specific crystal facets of UCNPs. Such a hetero-assembled DNA-AuNP/UCNP system maintains both plasmonic resonance of AuNPs and fluorescent properties of UCNPs, allowing targeted dual-modality imaging of cancer cells using an aptamer.

Light upconverting core–shell nanostructures: nanophotonic control for emerging applications

Nanophotonic control of light upconversion in the hierarchical core–shell nanostructures, their biomedical, solar energy and security encoding applications were reviewed.

Phospholipid-modified upconversion nanoprobe for ratiometric fluorescence detection and imaging of phospholipase D in cell lysate and in living cells

Phospholipase D (PLD) is a critical component of intracellular signal transduction and has been implicated in many important biological processes. It has been observed that there are abnormalities in PLD expression in many human cancers, and PLD is thus recognized as a potential diagnostic biomarker as well as a target for drug discovery. We report for the first time a phospholipid-modified nanoprobe for ratiometric upconversion fluorescence (UCF) sensing and bioimaging of PLD activity. The nanoprobe can be synthesized by a facile one-step self-assembly of a phospholipid monolayer composed of poly(ethylene glycol) (PEG)ylated phospholipid and rhodamine B-labeled phospholipid on the surface of upconversion nanoparticles (UCNPs) NaYF4: 20%Yb, 2%Er. The fluorescence resonance energy transfer (FRET) process from the UCF emission at 540 nm of the UCNPs to the absorbance of the rhodamine B occurs in the nanoprobe. The PLD-mediated hydrolysis of the phosphodiester bond makes rhodamine B apart from the UCNP surface, leading to the inhibition of FRET. Using the unaffected UCF emission at 655 nm as an internal standard, the nanoprobe can be used for ratiometric UCF detection of PLD activity with high sensitivity and selectivity. The PLD activity in cell lysates is also determined by the nanoprobe, confirming that PLD activity in a breast cancer cell is at least 7-fold higher than in normal cell. Moreover, the nanoprobe has been successfully applied to monitoring PLD activity in living cells by UCF bioimaging. The results reveal that the nanoprobe provides a simple, sensitive, and robust platform for point-of-care diagnostics and drug screening in biomedical applications.

Monodisperse lanthanide oxyfluorides LnOF (Ln = Y, La, Pr-Tm): morphology controlled synthesis, up-conversion luminescence and in vitro cell imaging

Lanthanide oxyfluorides LnOF (Ln = Y, La, Pr-Tm) nano/micro-materials with a variety of well-defined morphologies including nanorods, nanospindles, nanorod-bundles and nanospheres, have been successfully synthesized via a facile precipitation technique followed by a heating treatment. It is found that the pH values, fluoride sources and dosage of urea in the initial reaction systems play critical roles in the morphology determination of the LnOF products and the possible formation mechanism for these diverse architectures has been presented. XRD, FT-IR, TG-DTA, SEM, TEM, as well as up-conversion (UC) luminescence spectra are used to characterize the synthesized samples. Under 980 nm NIR laser excitation, red, green and blue UC luminescence are observed from Yb(3+)/Er(3+), Yb(3+)/Ho(3+) and Yb(3+)/Tm(3+) co-doped YOF nanospheres. The MTT assay indicates that YOF nanospheres exhibit good biocompatibility. Especially, the emission spectrum of YOF: 0.20Yb(3+), 0.04Er(3+) nanospheres is dominated by a single red emission at 660 nm, which falls into the "optical window" of biological tissues. The application of YOF: 0.20Yb(3+), 0.04Er(3+) nanospheres in the cell imaging is also investigated, which shows a bright-red emission without background noise.

Recent Advance of Biological Molecular Imaging Based on Lanthanide-Doped Upconversion-Luminescent Nanomaterials

Lanthanide-doped upconversion-luminescent nanoparticles (UCNPs), which can be excited by near-infrared (NIR) laser irradiation to emit multiplex light, have been proven to be very useful for in vitro and in vivo molecular imaging studies. In comparison with the conventionally used down-conversion fluorescence imaging strategies, the NIR light excited luminescence of UCNPs displays high photostability, low cytotoxicity, little background auto-fluorescence, which allows for deep tissue penetration, making them attractive as contrast agents for biomedical imaging applications. In this review, we will mainly focus on the latest development of a new type of lanthanide-doped UCNP material and its main applications for in vitro and in vivo molecular imaging and we will also discuss the challenges and future perspectives.

Upconversion nanoparticles for ratiometric fluorescence detection of nitrite

Individual upconversion nanoparticles with green and red emissions were synthesized and used as ratiometric fluorescence probes for the detection of nitrite by selectively turning on the green fluorescence.

Upconversion-nanophosphor-based functional nanocomposites

Upconversion nanophosphors have the ability to generate visible or near-infrared (NIR) emissions under continuous-wave NIR excitation. Utilizing this special photoluminescent properties, upconversion nanophosphors can be used as key components in complex nanocomposites for a wide range of applications. This review summarizes the basic concept, fabrication strategy, and typical application of upconversion-nanophosphor-based functional nanocomposites. The motivation to design these structures comes from the potential applications in detection, multi-modality bioimaging, and NIR light-induced therapy, as well as the tuning of the upconversion luminescence emissions. This review will give a brief summary of this rapidly developing field, and provide guidance to design and to fabricate new nanocomposites based on upconversion nanophosphors.

Shape-controlled ceria-based nanostructures for catalysis applications

Among oxide catalysts, ceria is a technologically important material because of its wide applications as a promoter in three-way catalysts for the elimination of toxic exhaust gases, low-temperature water-gas-shift reaction, oxygen sensors, oxygen permeation membrane systems, and fuel cells. The catalytic activities of cerium oxide are highly dependent on interfacial structures and nanocrystal morphologies. This Minireview highlights the recent progress in the research of ceria nanoshapes as both catalysts and catalyst supports, including the synthesis, structure characterization, catalytic properties, surface chemistry, as well as reaction mechanisms. Insights from in situ spectroscopy study and theoretical modeling of nanostructured ceria-based materials have shed light on the origin of the ceria shape effect. It is suggested that the surface structure of ceria controls the catalytic activity and selectivity through structure-dependent surface-site geometry, surface vacancy formation energy, defect sites, and coordinatively unsaturated sites on ceria. The morphology-dependent catalysis in ceria has offered a new strategy to finely tune the catalytic activity and selectivity through shape control without altering the catalyst composition. A brief summary and an outlook on this research field will be presented at the end.