Effect of structure, particle size and relative concentration of Eu(3+) and Tb(3+) ions on the luminescence properties of Eu(3+) co-doped Y(2)O(3):Tb nanoparticles

Luminescent CeO2:Eu3+ nanocrystals for robust in situ H2O2 real-time detection in bacterial cell cultures

Hydrogen peroxide (H2O2) quantification in biomedicine is valuable as inflammation biomarker but also in assays employing enzymes that generate or consume H2O2 linked to a specific biomarker. Optical H2O2 detection is typically performed through peroxidase-coupled reactions utilizing organic dyes that suffer, however, from poor stability/reproducibility and also cannot be employed in situ in dynamic complex cell cultures to monitor H2O2 levels in real-time. Here, we utilize enzyme-mimetic CeO2 nanocrystals that are sensitive to H2O2 and study the effect of H2O2 presence on their electronic and luminescent properties. We produce and dope with Eu3+ these particles in a single-step by flame synthesis and directly deposit them on Si and glass substrates to fabricate nanoparticle layers to monitor in real-time and in situ the H2O2 concentrations generated by Streptococcus pneumoniae clinical isolates. Furthermore, the small CeO2:Eu3+ nanocrystals are combined in a single-step with larger, non-responsive Y2O3:Tb3+ nanoparticles during their double-nozzle flame synthesis to engineer hybrid luminescent nanoaggregates as ratiometric robust biosensors. We demonstrate the functionality of these biosensors by monitoring their response in the presence of a broad range of H2O2 concentrations in vitro from S. pneumoniae, highlighting their potential for facile real-time H2O2 detection in vitro in cell cultures.

Aqueous dispersible green luminescent yttrium oxide:terbium microspheres with nanosilica shell coating

Tb-doped Y₂O₃ microspheres (MSs) were prepared via a homogeneous thermal degradation process at a low temperature and then coated with a nanosilica shell (Y₂O₃:Tb@SiO₂) using a sol-gel process. The core MSs were highly crystalline and spherical with a porous surface, single cubic phase, and particle size of 100-250 nm. Transmission electron microscopy (TEM) images clearly showed the spherical shape of the as-prepared core MSs, which were fully covered with a thick and mesoporous nanosilica shell. Fourier transform infrared (FTIR) spectra displayed the well-resolved infrared absorption peaks of silica (SiO, SiOSi, etc.), confirming the presence of the silica surface coating. The core MSs retained their spherical shape even after heat treatment and subsequent silica surface coating. It was observed that the core/shell MSs are easily dispersible in aqueous media and form a semi-transparent colloidal solution. Ultraviolet/visible and zeta potential studies were tested to prove the changes in the surface chemistry of the as-designed core/shell MSs and compare with their core counterpart. The growth of the amorphous silica shell not only increased the particle size but also enhanced remarkably the solubility and colloidal stability of the MSs in aqueous media. The strongest emission lines originating from the characteristic intra-shell 4f-4f electronic transitions of Tb ions were quenched after silica layer deposition, but the MSs still showed strong green (⁵D₄ → ⁷F₅ at 530-560 nm as most dominant) emission efficiency, which indicates great potential in fluorescent bio-probes. The emission intensity is discussed in relation to the quenching mechanism induced by surface silanol (Si-OH) groups, particle size, and surface charge.

Photoluminescence, thermoluminescence glow curve and emission characteristics of Y2O3:Er3+ nanophosphor

Nanocrystalline Er³⁺ doped Y₂O₃crystals were prepared by a sol gel technique. X-ray diffraction (XRD) patterns showed the cubic structure of Y₂O₃ and the crystallite size was found to be ~25nm. Optical absorption showed absorption peaks at 454, 495 and 521nm. These peaks are attributed to the ⁴F_3/2+⁴F_5/2, ⁴F_7/2 and ²H_11/2+⁴S_3/2 transitions of Er³⁺. Under excitation at 378nm, the appearance of strong green (520-565nm) down conversion emission assigned to the (²H_11/2,⁴S_3/2)→⁴I_15/2 transition and the feeble red (650-665nm) emission is assigned to the ⁴F_9/2→⁴I_15/2 transition. The color chromaticity coordinates showed emission in the green region. The strong green emission of Y₂O₃:Er³⁺ nanophosphor may be useful for applications in solid compact laser devices. Thermoluminescence (TL) studies of γ-irradiated Y₂O₃:Er³⁺ showed a prominent TL glow peak maximum at 383K along with a less intense shoulder peak at ~425K and a weak glow at 598K. TL emission peaks with maxima at 545, 490, 588 and 622nm for the doped sample were observed at a temperature of 383K and these emissions were due to defect related to the host material. TL kinetic parameters were calculated by a glow curve deconvolution (GCD) method and the obtained results are discussed in detail for their possible usage in high dose dosimetry.

Hydrothermal crystallization of a Ln2(OH)4SO4·nH2O layered compound for a wide range of Ln (Ln = La–Dy), thermolysis, and facile transformation into oxysulfate and oxysulfide phosphors

Ln-Dependent crystallization, structure, and thermolysis were systematically studied for layered Ln₂(OH)₄SO₄·nH₂O compounds, and their transformation into oxysulfate and oxysulfide phosphors was demonstrated.

Highly Enhanced Cooperative Upconversion Luminescence through Energy Transfer Optimization and Quenching Protection

Upconversion luminescence nanomaterials have shown great potential in biological and physical applications because of their unique properties. However, limited research exists on the cooperative sensitization upconversion emission in Tb(3+) ions over Er(3+) ions and Tm(3+) ions because of its low efficiency. Herein, by optimizing the doping ratio of sensitizer and activator to maximize the utilization of the photon energy and introducing the CaF2 inert shell to shield sensitizer from quenchers, we synthesize ultrasmall NaYbF4:Tb@CaF2 nanoparticles with a significant enhancement (690-fold) in cooperative sensitization upconversion emission intensity, compared with the parent NaYbF4:Tb. The lifetime of Tb(3+) emission in NaYbF4:Tb@CaF2 nanoparticles is prolonged extensively to ∼3.5 ms. Furthermore, NaYbF4:Tb@CaF2 was applied in in vitro and in vivo bioimaging. The presented luminescence enhancement strategy provides cooperative sensitization upconversion with new opportunities for bioapplication.

Hydrothermal conversion of layered hydroxide nanosheets into (Y0.95Eu0.05)PO4 and (Y0.96−xTb0.04Eux)PO4 (x = 0–0.10) nanocrystals for red and color-tailorable emission

Anion-exchange of NO₃⁻-LRH nanosheets with phosphate has led to (Y,Tb,Eu)PO₄ nanocrystals showing color-tailorable emissions.

(Y,Tb,Eu)2O3 monospheres for highly fluorescent films and transparent hybrid films with color tunable emission

(Y,Tb,Eu)₂O₃ monospheres were employed as building blocks for highly fluorescent films and as dispersion fillers for transparent polymer films.

Structural and Luminescence Properties of Lu₂O₃:Eu3+ F127 Tri-Block Copolymer Modified Thin Films Prepared by Sol-Gel Method

Lu₂O₃:Eu³⁺ transparent, high density, and optical quality thin films were prepared using the sol-gel dip-coating technique, starting with lutetium and europium nitrates as precursors and followed by hydrolysis in an ethanol-ethylene glycol solution. Acetic acid and acetylacetonate were incorporated in order to adjust pH and as a sol stabilizer. In order to increment the thickness of the films and orient the structure, F127 Pluronic acid was incorporated during the sol formation. Structural, morphological, and optical properties of the films were investigated for different F127/Lu molar ratios (0–5) in order to obtain high optical quality films with enhanced thickness compared with the traditional method. X-ray diffraction (XRD) shows that the films present a highly oriented cubic structure <111> beyond 1073 K for a 3-layer film, on silica glass substrates. The thickness, density, porosity, and refractive index evolution of the films were investigated by means of m-lines microscopy along with the morphology by scanning electron microscope (SEM) and luminescent properties.

Layered rare-earth hydroxide and oxide nanoplates of the Y/Tb/Eu system: phase-controlled processing, structure characterization and color-tunable photoluminescence via selective excitation and efficient energy transfer

Well-crystallized (Y_0.97-x Tb_0.03Eu _x )₂(OH)₅NO₃·nH₂O (x = 0-0.03) layered rare-earth hydroxide (LRH) nanoflakes of a pure high-hydration phase have been produced by autoclaving from the nitrate/NH₄OH reaction system under the optimized conditions of 100 °C and pH ∼7.0. The flakes were then converted into (Y_0.97-x Tb_0.03Eu _x )₂O₃ phosphor nanoplates with color-tunable photoluminescence. Detailed structural characterizations confirmed that LRH solid solutions contained NO₃^- anions intercalated between the layers. Characteristic Tb³⁺ and Eu³⁺ emissions were detected in the ternary LRHs by selectively exciting the two types of activators, and the energy transfer from Tb³⁺ to Eu³⁺ was observed. Annealing the LRHs at 1100 °C produced cubic-lattice (Y_0.97-x Tb_0.03Eu _x )₂O₃ solid-solution nanoplates with exposed 222 facets. Multicolor, intensity-adjustable luminescence was attained by varying the excitation wavelength from ∼249 nm (the charge transfer excitation band of Eu³⁺) to 278 nm (the 4f⁸-4f⁷5d¹ transition of Tb³⁺). Unitizing the efficient Tb³⁺ to Eu³⁺ energy transfer, the emission color of (Y_0.97-x Tb_0.03Eu _x )₂O₃ was tuned from approximately green to yellowish-orange by varying the Eu³⁺/Tb³⁺ ratio. At the optimal Eu³⁺ content of x = 0.01, the efficiency of energy transfer was ∼91% and the transfer mechanism was suggested to be electric multipole interactions. The phosphor nanoplates developed in this work may be incorporated in luminescent films and find various lighting and display applications.

Preparation and scintillating properties of Sol-Gel Eu(3+), TB(3+) co-doped Lu(2)O(3) nanopowders

Nanocrystalline Eu³⁺, Tb³⁺ co-doped Lu₂O₃ powders with a maximum size of 25.5 nm were prepared by the sol-gel process, using lutetium, europium and terbium nitrates as precursors, and ethanol as a solvent. Differential thermal analysis (DTA) and infrared spectroscopy (IR) were used to study the chemical changes during the xerogel annealing. After the sol evaporation at 100 °C, the formed gel was annealed from 300 to 900 °C for 30 min under a rich O₂ atmosphere, and the yielded product was analyzed by X-ray diffraction (XRD) to characterize the microstructural behavior and confirm the crystalline structure. The results showed that Lu₂O₃ nanopowders start to crystallize at 400 °C and that the crystallite size increases along with the annealing temperature. A transmission electron microscopy (TEM) study of samples annealed at 700 and 900 °C was carried out in order to analyze the microstructure, as well as the size, of crystallites. Finally, in regard to scintillating properties, Eu³⁺ dopant (5 mol%), Tb³⁺ codoped Lu₂O₃ exhibited a typical red emission at 611 nm (D_°→⁷F₂), furthermore, the effect of Tb³⁺ molar content (0.01, 0.015 and 0.02% mol) on the Eu³⁺ radioluminiscence was analyzed and it was found that the higher emission intensity corresponds to the lower Tb³⁺ content.

Color-tunable nanophosphors by co-doping flame-made Y2O3 with Tb and Eu

Rare-earth phosphors with tunable optical properties are used in display panels and fluorescent lamps and have potential applications in lasers and bio-imaging. Here, non-aggregated Y2O3 nanocrystals either doped with Tb3+ (1-5 at%) or co-doped with Tb3+ (2 at%) and Eu3+ (0.1-2 at%) ions are made in one-step by scalable flame spray pyrolysis. The morphology of these nanophosphors is investigated by X-ray diffraction, electron microscopy and N2 adsorption while their optical properties are monitored by photoluminescent spectroscopy. When yttria nanocrystals are doped with terbium, a bright green emission is obtained at an optimum Tb-content of 2 at%. When, however, europium is added, the emission color of these Tb-doped yttria nanophosphors can be tuned precisely from green to red depending on the Tb/Eu ratio. Furthermore, energy-transfer from Tb3+ to Eu3+ is observed, thus allowing the control of the excitation spectra of the co-doped nanophosphors.

Synthesis and Cytotoxicity of Y(2)O(3) Nanoparticles of Various Morphologies

As the field of nanotechnology continues to grow, evaluating the cytotoxicity of nanoparticles is important in furthering their application within biomedicine. Here, we report the synthesis, characterization, and cytotoxicity of nanoparticles of different morphologies of yttrium oxide, a promising material for biological imaging applications. Nanoparticles of spherical, rod-like, and platelet morphologies were synthesized via solvothermal and hydrothermal methods and characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), light scattering, surface area analysis, thermogravimetric analysis (TGA), and zeta potential measurements. Nanoparticles were then tested for cytotoxicity with human foreskin fibroblast (HFF) cells, with the goal of elucidating nanoparticle characteristics that influence cytotoxicity. Cellular response was different for the different morphologies, with spherical particles exhibiting no cytotoxicity to HFF cells, rod-like particles increasing cell proliferation, and platelet particles markedly cytotoxic. However, due to differences in the nanoparticle chemistry as determined through the characterization techniques, it is difficult to attribute the cytotoxicity responses to the particle morphology. Rather, the cytotoxicity of the platelet sample appears due to the stabilizing ligand, oleylamine, which was present at higher levels in this sample. This study demonstrates the importance of nanoparticle chemistry on in vitro cytotoxicity, and highlights the general importance of thorough nanoparticle characterization as a prerequisite to understanding nanoparticle cytotoxicity.