Rare Earth Fluoride Nanocrystals Research Articles

Efficient up-conversion red emission from TiO2:Yb,Er nanocrystals.

Usually, up-conversion (UC) green emission is easily observed by using rare-earth doped fluoride nanocrystals. However, preferential red emission is desired for some actual applications especially in biological field. Here, we demonstrated that the dominant UC red emission can be realized by preparing TiO2:Yb,Er nanocrystals under 980 nm exciation. By controlling the crystal symmetry and size via the annealing temperature and Yb3+ ions concentration, the enhanced UC red emission is achieved. The multi-photon relaxation and cross-relaxation mechanisms may be responsible for the energy transform process and in turn the UC emission.

Microwave–assisted synthesis of water–disperse and biocompatible NaGdF4: Yb,Ln@NaGdF4 nanocrystals for UCL/CT/MR multimodal imaging

In this paper, we have developed a series of rare earth fluoride nanocrystals (NCs) that can be used for multimodal imaging applications. Three highly monodisperse and water dispersible NaGdF4:Yb,Ln@NaGdF4 (Ln=Er, Tm, Ho) upconversion luminescence (UCL) NCs with an average size of 75nm were prepared using a facile and efficient microwave–assisted solvothermal reaction in ethylene glycol (EG). The morphology, crystal structures, size distributions and zeta potentials of the resulting NCs were fully characterized by transmission electron microscopy (TEM), X–ray diffraction (XRD) and Nano–ZS90 Zetasizer. The obtained NaGdF4:Yb,Ln@NaGdF4 (Ln=Er, Tm, Ho) NCs could emit bright blue, green and red luminescence in water upon laser excitation at 980nm. Furthermore, these core–shell NCs exhibited low cytotoxicity for HeLa and C9H2 cells, separately. Moreover, these NCs also displayed excellent Hounsfield units (HU) values in X–ray computed tomography (CT) imaging and high relaxivity parameters (r1) in magnetic resonance (MR) imaging in vitro. Thus, these small, water–dispersible and biocompatible NCs show excellent potential as contrast agents for UCL/CT/MR multimodal imaging and other biomedical applications.

A semi-combinatorial approach for investigating polycatenar ligand-controlled synthesis of rare-earth fluoride nanocrystals.

Rare-earth nanocrystals (RE NCs) are a valuable class of nanomaterials due to their ability to bring the attractive properties of rare earth bulk crystals to biomedical applications and solution-processable engineering. Of the bottom-up synthesis approaches, solvothermal methods yield highly crystalline and monodisperse RE NCs. Herein, we report a polycatenar ligand controlled synthesis of RE NCs using a semi-combinatorial approach with a microreactor setup that enables the investigation of the influences of several reaction parameters on the growth of the RE NCs. This approach enabled the discovery of conditions that yield highly monodisperse elongated plates with neutral, positive, and negative curvatures, as well as provide evidence of the formation of chiral morphologies.

Europium‐activated rare earth fluoride (LnF3:Eu3+–Ln = La, Gd) nanocrystals prepared by using ionic liquid/NH4F as a fluorine source via hydrothermal synthesis

AbstractLanthanide (Ln) fluorides are considered exceptional luminescent rigid host matrices for various optical active Ln3+ ions due to their high refractive index, high chemical stability and low phonon energy, leading to the low probability of non‐radiative decay, which results in higher photoluminescence quantum yield (PLQY) (usually higher than oxide hosts). In this study, Eu3+‐activated Ln fluorides (LnF3:Eu3+–Ln = La, Gd) are synthesized by the hydrothermal method using 1‐butyl‐3‐methylimidazolium tertrafluoroborate [BMIBF4] and NH4F as fluorine precursors. The synthesized nanocrystals (NCs) are structurally and morphologically characterized, and their optical properties investigated using spectrofluorometry. The X‐ray diffraction (XRD) patterns of Eu3+‐substituted and ‐unsubstituted LnF3 (prepared from a different fluorine source) are indexed based on the hexagonal and orthorhombic crystal structure, respectively. Average crystalline sizes are calculated using the Scherrer equation and it is found that the synthesized NCs have an average crystalline size of 12–35 nm. Transmission electron microscopy (TEM) images reveal that the NCs are well dispersed and nearly ellipsoid, with an average size of ~ 5 nm. Eu3+‐activated NCs show characteristic excitation and emission spectra. The emission spectra show both magnetic (5D0–7F1) and electric (5D0–7F2) dipole transition with appropriate CIE color coordinates; however, the intensity of the magnetic dipole transition is high, which is in accordance with local site symmetry. Owing to their unique size and excellent optical properties, the synthesized NCs may have potential application in the fields bio‐imaging and solar concentrators. Copyright © 2016 John Wiley & Sons, Ltd.

Sr2+ and Tb3+ doping tuning the size, morphology, and photoluminescence of NaCeF4 nanorods via solvothermal method

Doping for nanocrystalline materials is of fundamental importance in tuning the size, phase, morphology and relational properties, such as fluorescence of rare earth fluoride nanocrystals. Here, we report hexagonal NaCeF4 nanorods with controlled size, morphology and photoluminescence were synthesized via solvothermal method by Sr2+ doping as well as Tb3+ doping. Transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) results illustrated Sr2+ which occupies Na+ site partially is crucial in controlling nanorods’ morphology, size, and emission intensity. The doping of Tb3+ as activation center can also play key role to tune the morphology of NaCeF4 nanorods containing Sr2+ from long nanobars to hexagonal prisms. Growth process revealed that ultrasmall SrF2 nanocrystals with cubic shape were fabricated firstly, and then Sr2+ doped NaCeF4 nanorods were obtained by oriented attachment and Ostwald ripening. The emission intensity was not only decided by Tb3+ doping concentration, but also morphology-dependent.

Shape-Controlled Synthesis of Isotopic Yttrium-90-Labeled Rare Earth Fluoride Nanocrystals for Multimodal Imaging.

Isotopically labeled nanomaterials have recently attracted much attention in biomedical research, environmental health studies, and clinical medicine because radioactive probes allow the elucidation of in vitro and in vivo cellular transport mechanisms, as well as the unambiguous distribution and localization of nanomaterials in vivo. In addition, nanocrystal-based inorganic materials have a unique capability of customizing size, shape, and composition; with the potential to be designed as multimodal imaging probes. Size and shape of nanocrystals can directly influence interactions with biological systems, hence it is important to develop synthetic methods to design radiolabeled nanocrystals with precise control of size and shape. Here, we report size- and shape-controlled synthesis of rare earth fluoride nanocrystals doped with the β-emitting radioisotope yttrium-90 ((90)Y). Size and shape of nanocrystals are tailored via tight control of reaction parameters and the type of rare earth hosts (e.g., Gd or Y) employed. Radiolabeled nanocrystals are synthesized in high radiochemical yield and purity as well as excellent radiolabel stability in the face of surface modification with different polymeric ligands. We demonstrate the Cerenkov radioluminescence imaging and magnetic resonance imaging capabilities of (90)Y-doped GdF3 nanoplates, which offer unique opportunities as a promising platform for multimodal imaging and targeted therapy.

Visualization of melanoma tumor with lectin-conjugated rare-earth doped fluoride nanocrystals.

AimTo develop specific fluorescent markers for melanoma tumor visualization, which would provide high selectivity and reversible binding pattern, by the use of carbohydrate-recognizing proteins, lectins, combined with the physical ability for imaging deep in the living tissues by utilizing red and near infrared fluorescent properties of specific rare-earth doped nanocrystals (NC).MethodsB10F16 melanoma cells were inoculated to C57BL/6 mice for inducing experimental melanoma tumor. Tumors were removed and analyzed by lectin-histochemistry using LABA, PFA, PNA, HPA, SNA, GNA, and NPL lectins and stained with hematoxylin and eosin. NPL lectin was conjugated to fluorescent NaGdF4:Eu3+-COOH nanoparticles (5 nm) via zero length cross-linking reaction, and the conjugates were purified from unbound substances and then used for further visualization of histological samples. Fluorescent microscopy was used to visualize NPL-NaGdF4:Eu3+ with the fluorescent emission at 600-720 nm range.ResultsNPL lectin selectively recognized regions of undifferentiated melanoblasts surrounding neoangiogenic foci inside melanoma tumor, PNA lectin recognized differentiated melanoblasts, and LCA and WGA were bound to tumor stroma regions. NPL-NaGdF4:Eu3+ conjugated NC were efficiently detecting newly formed regions of melanoma tumor, confirmed by fluorescent microscopy in visible and near infrared mode. These conjugates possessed high photostability and were compatible with convenient xylene-based mounting systems and preserved intensive fluorescent signal at samples storage for at least 6 months.ConclusionNPL lectin-NaGdF4:Eu3+ conjugated NC permitted distinct identification of contours of the melanoma tissue on histological sections using red excitation at 590-610 nm and near infrared emission of 700-720 nm. These data are of potential practical significance for development of glycans-conjugated nanoparticles to be used for in vivo visualization of melanoma tumor.

Hydrothermal synthesis, characterization and up/down-conversion luminescence of barium rare earth fluoride nanocrystals

Mixed hydrothermal system H2O–OA (EDA)–O-A(LO-A) is developed to synthesize barium rare earth fluorides nanocrystals (OA=oleylamine, EDA=ethylenediamine, O-A=oleic acid and LO-A=linoleic acid). They are presented as BaREF5 (RE=Ce, Pr, Nd, Eu, Gd, Tb, Dy, Y, Tm, Lu) and Ba2REF7 (RE=La, Sm, Ho, Er, Yb). The influence of reaction parameters (rare earth species, hydrothermal system and temperature) is checked on the phase and shape evolution of the fluoride nanocrystals. It is found that reaction time and temperature of these nanocrystals using EDA (180°C, 6h) is lower than those of them using OA (220°C, 10h). The photoluminescence properties of these fluorides activated by some rare earth ions (Nd3+, Eu3+, Tb3+) are studied, and especially up-conversion luminescence of the four fluoride nanocrystal systems (Ba2LaF7:Yb, Tm(Er), Ba2REF7:Yb, Tm(Er) (RE=Gd, Y, Lu)) is observed.

Hydrogels dispersed by doped rare earth fluoride nanocrystals: Ionic liquid dispersion and down/up-conversion luminescence

Two typical kinds of rare earth fluoride nanocrystals codoped with rare earth ions (Eu3+ and Tm3+/Er3+,Yb3+) are synthesized and dispersed in ionic liquid compound (1-chlorohexane-3-methylimidazolium chloride, abbreviated as [C6mim][Cl]). Assisted by agarose, the luminescent hydrogels are prepared homogeneously. The down/up-conversion luminescence of these hydrogels can be realized for the dispersed rare earth fluoride nanocrystals. The results provide a strategy to prepare luminescent (especially up-conversion luminescent) hydrogels with ionic liquid to disperse rare earth fluoride nanocrystals.

Luminescent Hybrid Ionogels Functionalized with rare Earth fluoride Up‐conversion Nanocrystals Dispersing in Ionic Liquid

Rare earth doped fluorides (BaMgF4, aYF4 and BaYF5/BaLuF5) have been synthesized and dispersed in an ionic liquid compound, (3-triethoxysilyl) propyl-3-methylimidazolium chloride (denoted as IM(+)Cl(-)). Through the cohydrolysis and copolycondensatoin reaction between the alkoxy group (3-triethoxysilyl) of IM(+) and tetraethoxysilane in the presence of carboxylic acids (formic acid) as catalyst and water source, luminescent hybrid ionogels form subsequently. (1)H NMR spectroscopy, X-ray diffraction, transmission electron microscopy, scanning electron microscopy and especially up-conversion (UC) luminescence spectroscopy are used to characterize the precursors and the resulted hybrid ionogels. These hybrid ionogels exhibit the UC luminescence properties of immobilized rare earth fluoride nanocrystals (BaMgF4, NaYF4 and BaYF5/BaLuF5) doped Er(3+)/Tm(3+), Yb(3+).

Barium rare earth fluoride nanocrystals: high temperature solution synthesis, characterization and luminescence

A high temperature solution system with BaCO3/RECl3·xH2O in oleic acid/1-octadecene has been developed to prepare barium rare earth fluoride nanocrystals: tetragonal phase of BaREF5 (RE = Pr, Nd, Eu, Tb, Dy, Tm, Lu, Y), pure cubic phase Ba2REF7 (RE = La, Sm, Ho, Er, Yb), and BaREF5 (RE = Ce, Gd) colloidal nanocrystals. In addition, it is proved that the functionalization of these nanocrystals by means of doping with Eu, Tb, and Yb, Er/Tm ion pair can obtain red, green, and visible-to-the-naked-eye green/blue upconversion emissions.

Phase‐ and Size‐Controllable Synthesis of Hexagonal Upconversion Rare‐Earth Fluoride Nanocrystals through an Oleic Acid/Ionic Liquid Two‐Phase System

Herein, we introduce a facile, user- and environmentally friendly (n-octanol-induced) oleic acid (OA)/ionic liquid (IL) two-phase system for the phase- and size-controllable synthesis of water-soluble hexagonal rare earth (RE = La, Gd, and Y) fluoride nanocrystals with uniform morphologies (mainly spheres and elongated particles) and small sizes (<50 nm). The unique role of the IL 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF(6)) and n-octanol in modulating the phase structure and particle size are discussed in detail. More importantly, the mechanism of the (n-octanol-induced) OA/IL two-phase system, the formation of the RE fluoride nanocrystals, and the distinctive size- and morphology-controlling capacity of the system are presented. BmimPF(6) is versatile in term of crystal-phase manipulation, size and shape maintenance, and providing water solubility in a one-step reaction. The luminescent properties of Er(3+)-, Ho(3+)-, and Tm(3+)-doped LaF(3), NaGdF(4), and NaYF(4) nanocrystals were also studied. It is worth noting that the as-prepared products can be directly dispersed in water due to the hydrophilic property of Bmim(+) (cationic part of the IL) as a capping agent. This advantageous feature has made the IL-capped products favorable in facile surface modifications, such as the classic Stober method. Finally, the cytotoxicity evaluation of NaYF(4):Yb,Er nanocrystals before and after silica coating was conducted for further biological applications.

Raisin-like rare earth doped gadolinium fluoride nanocrystals: microwave synthesis and magnetic and upconversion luminescent properties

Bifunctional lanthanide doped 3D raisin-like GdF3 nanocrystals were synthesized by a microwave method. The influences of synthesis parameters on the final morphology were investigated and the morphology can be tuned to snow-like microcrystals and nanocrystals. The as-prepared samples possess properties of multicolor upconversion (UC) photoluminescence (PL) and paramagnetism. To understand the magnetic mechanism, temperature dependence of zero-field cooling (ZFC) and field cooling (FC) magnetization of the raisin-like GdF3 nanocrystals were studied.

Bioimaging and toxicity assessments of near-infrared upconversion luminescent NaYF 4:Yb,Tm nanocrystals

In vitro or in vivo bioimaging utilizing the upconversion (UC) luminescence of rare earth fluoride nanocrystals (NCs) has attracted much attention, especially for Yb 3+/Tm 3+ doped NCs with a near-infrared (NIR) UC emission at 800 nm. Herein, water-soluble NaYF 4:Yb,Tm NCs with strong NIR UC emission were synthesized with a solvothermal method. In vitro and in vivo bioimaging and toxicity assessments were carried out with HeLa cell and Caenorhabditis elegans ( C. elegans) cases, respectively. NaYF 4:Yb,Tm NCs afforded an efficient NIR image of the HeLa cells with an incubation concentration of 10 μg mL −1, and CCK-8 assay revealed a low cytotoxicity. Fed with Escherichia coli ( E. coli) and NCs together, the C. elegans showed a NIR image in the gut from the pharynx to the anus. Further, these NCs could be excreted out when those worms were then fed with only E. coli. Toxicity studies were further addressed with protein expression, life span, egg production, egg viability, and growth rate of the worms in comparison with those of the intact ones. The feeding of rare earth fluoride NCs with a dose of 100 μg does not arise obvious toxicity effect from the growth to procreation. The in vitro and in vivo studies confirm that NaYF 4:Yb,Tm NCs could be served as an excellent NIR emission bioprobe with low toxicity.

A new General Strategy for the Synthesis of Upconversion Rare Earth Fluoride Nanocrystals under Mild Conditions

A new General Strategy for the Synthesis of Upconversion Rare Earth Fluoride Nanocrystals under Mild Conditions

One‐Pot Synthesis of Carboxyl‐Functionalized Rare Earth Fluoride Nanocrystals with Monodispersity, Ultrasmall Size and Very Bright Luminescence

AbstractWe demonstrated a straightforward approach to the synthesis of ultrasmall, monodisperse and carboxyl‐functionalized rare earth (RE) fluoride nanocrystals via a one‐pot reaction by introducing poly(acrylic acid) (PAA) as a coordination agent and surfactant. The morphologies, crystal structure, surface groups, and luminescent properties of the PAA‐capped RE fluoride nanocrystals were investigated in detail by TEM, FTIR, and photoluminescence spectroscopy. The obtained RE fluoride nanocrystals were ultrasmall in size, monodisperse, and highly crystalline. FTIR spectra confirmed that the PAA molecules strongly coordinated to the surface of the nanocrystals, which allows the formation of transparent colloidal aqueous solutions. Successful coating of the LaF3 shell on the NaCeF4:Tb3+ nanocrystals can increase the luminescence efficiency and lifetimes of Tb3+ ions relative to the pure NaCeF4:Tb3+ core. This synthesis procedure could become a versatile approach for the straightforward synthesis of carboxyl‐functionalized nanocrystals with ultrasmall size and monodispersity.

Efficient manganese luminescence induced by Ce3+-Mn2+ energy transfer in rare earth fluoride and phosphate nanocrystals.

Manganese materials with attractive optical properties have been proposed for applications in such areas as photonics, light-emitting diodes, and bioimaging. In this paper, we have demonstrated multicolor Mn2+ luminescence in the visible region by controlling Ce3+-Mn2+ energy transfer in rare earth nanocrystals [NCs]. CeF3 and CePO4 NCs doped with Mn2+ have been prepared and can be well dispersed in aqueous solutions. Under ultraviolet light excitation, both the CeF3:Mn and CePO4:Mn NCs exhibit Mn2+ luminescence, yet their output colors are green and orange, respectively. By optimizing Mn2+ doping concentrations, Mn2+ luminescence quantum efficiency and Ce3+-Mn2+ energy transfer efficiency can respectively reach 14% and 60% in the CeF3:Mn NCs.

Mesoporous rare earth fluoride nanocrystals and their photoluminescence properties

YF 3 and YF 3:Eu 3+ mesoporous hexagonal nanocrystals were successfully synthesized via a simple hydrothermal process based on the in situ assembly of the as-synthesized YF 3 and YF 3:Eu 3+ nanoparticles. The well defined mesoporous nanostructures are formed by phenanthroline assisted assembly of ∼20 nm nanoparticles, and 2–4 nm pores are contained as indicated by N 2 adsorption–desorption studies. The obtained YF 3:Eu 3+ mesoporous hexagonal nanoplates show a significant photoluminescence intensity enhancement compared with other shaped YF 3:Eu 3+ nanocrystals.

A general strategy for the synthesis of upconversion rare earth fluoride nanocrystals via a novel OA/ionic liquid two-phase system

Herein we report a general strategy to synthesize highly uniform and monodisperse rare earth fluoride nanocrystals through a novel OA/ionic liquid two-phase system, while water-soluble hexagonal NaREF(4) nanocrystals are obtained by adding n-octanol.

Morphology of NaNdF 4 nanocrystals from Nd(C 3H 7COO) 3·Phen and Nd(NO 3) 3·Phen (Phen, 1,10-phenanthroline) as neodymium precursors

A series of NaNdF 4 nanocrystals was synthesized via a facile hydrothermal route with Nd(C 3H 7COO) 3·Phen and Nd(NO 3) 3·Phen (Phen, 1,10-phenanthroline) as the Nd precursors. Distinct effect of the neutral donor ligand (Phen) on the morphology of NaNdF 4 nanocrystals was demonstrated. When Nd(C 3H 7COO) 3·Phen was chosen and the hydrothermal reaction temperature was controlled at 220 °C, the NaNdF 4 nanocrystals with uniform short nanorod shape were obtained. The sizes of the as-prepared nanorods could be tuned by changing the hydrothermal temperatures. This method provided a useful way for the preparation of sodium rare-earth fluoride nanocrystals with controlled shapes and sizes.