Temperature-Induced Structural Transformations in Undoped and Eu3+-Doped Ruddlesden–Popper Phases Sr2SnO4 and Sr3Sn2O7: Relation to the Impedance and Luminescence Behaviors

We report that luminescence of Eu3+ ion incorporated into Ruddlesden–Popper phases allows monitoring phase transition in powders (instead of single crystals), in a time-efficient manner (compared to neutron diffraction), and importantly, with greater sensitivity than previous methods. Crystal structure and dielectric response of undoped and 0.5%Eu3+-doped Sr3Sn2O7 ceramics were studied as a function of temperature over the temperature range of 300–800 K. The luminescence studies of 0.5%Eu3+-doped Sr2SnO4 and Sr3Sn2O7 samples were performed in the temperature range of 80–500 K. These results were compared with the respective dependences for the undoped compounds. The structural transformations in 0.5%Eu3+-doped Sr3Sn2O7 were found at 390 and 740 K. The former is associated with the isostructural atomic rearrangement that resulted in a negative thermal expansion along two of three orthorhombic crystallographic axes, while the latter corresponds to the structural transition from the orthorhombic Amam phase to the tetragonal I4/mmm one. A similar temperature behavior with the structural transformations in the same temperature ranges was observed in undoped Sr3Sn2O7, although the values of lattice parameters of the Eu3+-doped and undoped compounds were found to be slightly different indicating an incorporation of europium in the crystal lattice. A dielectric anomaly associated with a structural phase transition was observed in Sr3Sn2O7 at 390 K. Optical measurements performed over a wide temperature range demonstrated a clear correlation between structural transformations in Eu3+-doped Sr2SnO4 and Sr3Sn2O7 and the temperature anomalies of their luminescence spectra, suggesting the efficacy of this method for the determination of subtle phase transformations

Optical Properties Investigation of Upconverting K₂Gd(PO₄)(WO₄):20%Yb³⁺,Tm³⁺ Phosphors

Nowadays, scientists are interested in inorganic luminescence materials that can be excited with UV or NIR radiation and emit in the visible range. Such inorganic materials can be successfully used as luminescent or anti-counterfeiting pigments. In this work, we report the synthesis and optical properties investigation of solely Tm3+ doped and Yb3+/Tm3+ co-doped K2Gd(PO4)(WO4) phosphors. The single-phase samples were prepared using a solid-state reaction method. The Tm3+ concentration was changed from 0.5% to 5%. Downshifting and upconversion emission studies were performed under 360 nm and 980 nm excitation, respectively. Yb3+ ions were used as sensitizers in the K2Gd(PO4)(WO4) phosphors to transfer the captured energy to Tm3+ ions. It turned out that under UV excitation, phosphors emitted in the blue spectral area regardless of the presence or absence of Yb3+. However, a very strong deep-red (~800 nm) emission was observed when Yb3+ and Tm3+-containing samples were excited with a 980 nm wavelength laser. It is interesting that the highest upconversion emission in the UV/Visible range was achieved for 20% Yb3+, 0.5% Tm3+ doped sample, whereas the sample co-doped with 20% Yb3+, 2% Tm3+ showed the most intensive UC emission band in the NIR range. The materials were characterized using powder X-ray diffraction and scanning electron microscopy. Optical properties were studied using steady-state and kinetic downshifting and upconversion photoluminescence spectroscopy

Luminescence and Luminescence Quenching of K₂Bi(PO₄)(MoO₄):Eu³⁺ Phosphors with Efficiencies Close to Unity

A very good light emitting diode (LED) phosphor must have strong absorption, high quantum efficiency, high color purity, and high quenching temperature. Our synthesized K₂Bi­(PO₄)­(MoO₄):Eu³⁺ phosphors possess all of the mentioned properties. The excitation of these phosphors with the near-UV or blue radiation results in a bright red luminescence dominated by the ⁵D₀ → ⁷F₂ transition at ∼615 nm. Color coordinates are very stable when changing Eu³⁺ concentration or temperature in the range of 77–500 K. Furthermore, samples doped with 50% and 75% Eu³⁺ showed quantum efficiencies close to 100% which is a huge benefit for practical application. Temperature dependent luminescence measurements showed that phosphor performance increases with increasing Eu³⁺ concentration. K₂Eu­(PO₄)­(MoO₄) sample at 400 K lost only 20% of the initial intensity at 77 K and would lose half of the intensity only at 578 K. Besides, the ceramic disks with thicknesses of 0.33 and 0.89 mm were prepared from K₂Eu­(PO₄)­(MoO₄) powder, and it turned out that they efficiently converted the radiation of 375 nm LED to the red light. The conversion of 400 nm LED radiation to the red light was not complete; thus, the light sources with various tints of purple color were obtained. The combination of ceramic disks with 455 nm LED yielded the light sources with tints of blue color due to the low absorption of ceramic disk in this spectral range. In addition, these phosphors possess a very unique emission spectra; thus, they could also be applied in luminescent security pigments

Hydrothermal Synthesis of Well-Defined Red-Emitting Eu-Doped GdPO4 Nanophosphors and Investigation of Their Morphology and Optical Properties

Rare-earth-doped GdPO4 nanoparticles have recently attracted much scientific interest due to the simultaneous optical and magnetic properties of these materials and their possible application in bio-imaging. Herein, we report the hydrothermal synthesis of GdPO4:Eu3+ nanoparticles by varying different synthesis parameters: pH, <Gd>:<P> molar ratio, and Eu3+ concentration. It turned out that the Eu3+ content in the synthesized nanoparticles had little effect on particle shape and morphology. The synthesis media pH, however, has showed a pronounced impact on particle size and distribution, i.e., the nanoparticle length can be adjusted from hundreds to tens of nanometers by changing the pH from 2 to 11, respectively. Increasing the <Gd>:<P> molar ratio resulted in a decrease in nanoparticle length and an increase in its width. The temperature-dependent measurements in the 77–500 K range revealed that the GdPO4:50%Eu3+ sample maintains half of its emission intensity, even at room temperature (TQ1/2 = 291 ± 19 K)

Hydrothermal Synthesis of Well-Defined Red-Emitting Eu-Doped GdPO₄ Nanophosphors and Investigation of Their Morphology and Optical Properties

Rare-earth-doped GdPO4 nanoparticles have recently attracted much scientific interest due to the simultaneous optical and magnetic properties of these materials and their possible application in bio-imaging. Herein, we report the hydrothermal synthesis of GdPO4:Eu3+ nanoparticles by varying different synthesis parameters: pH, : molar ratio, and Eu3+ concentration. It turned out that the Eu3+ content in the synthesized nanoparticles had little effect on particle shape and morphology. The synthesis media pH, however, has showed a pronounced impact on particle size and distribution, i.e., the nanoparticle length can be adjusted from hundreds to tens of nanometers by changing the pH from 2 to 11, respectively. Increasing the : molar ratio resulted in a decrease in nanoparticle length and an increase in its width. The temperature-dependent measurements in the 77–500 K range revealed that the GdPO4:50%Eu3+ sample maintains half of its emission intensity, even at room temperature (TQ1/2 = 291 ± 19 K)

Synthesis and Study of Thermoresponsive Amphiphilic Copolymers via RAFT Polymerization

Synthesis and study of well-defined thermoresponsive amphiphilic copolymers with various compositions were reported. Kinetics of the reversible addition-fragmentation chain transfer (RAFT) (co)polymerization of styrene (St) and oligo(ethylene glycol) methyl ether methacrylate (PEO5MEMA) was studied by size exclusion chromatography (SEC) and 1H NMR spectroscopy, which allows calculating not only (co)polymerization parameters but also gives valuable information on RAFT (co)polymerization kinetics, process control, and chain propagation. Molecular weight Mn and dispersity Đ of the copolymers were determined by SEC with triple detection. The detailed investigation of styrene and PEO5MEMA (co)polymerization showed that both monomers prefer cross-polymerization due to their low reactivity ratios (r1 2 p(St-co-PEO5MEMA) with various compositions is almost ideally statistical or azeotropic. The thermoresponsive properties of p(St-co-PEO5MEMA) copolymers in aqueous solutions as a function of different hydrophilic/hydrophobic substituent ratios were evaluated by measuring the changes in hydrodynamic parameters under applied temperature using the dynamic light scattering method (DLS)

Temperature-Dependent Luminescence of Red-Emitting Ba2Y5B5O17: Eu3+ Phosphors with Efficiencies Close to Unity for Near-UV LEDs

International audienc

Characterization and stability study of cranberry flavonoids in lipid liquid crystalline systems

The main objective of the present study was to investigate mixtures of soy phosphatidylcholine (SPC) and glycerol dioleate (GDO) as encapsulation matrices for cranberry flavonoids. The effects of flavonoids loading into non-aqueous formulations, non-lamellar liquid crystalline phases, and their colloidal dispersions were studied by using synchrotron small angle X-ray diffraction, dynamic light scattering. Flavonoids incorporation is discussed with respect to the lipid aggregation behavior, self-assembled nanostructure, and chemical stability by using antioxidant activity assay. The obtained results show that SPC/GDO-based formulations can incorporate relatively high amounts of flavonoids and serve as liquid crystalline delivery vehicles in the form of bulk phases or colloidal dispersions. Practical applications: Our results show that SPC/GDO-based formulations can incorporate relatively high amounts of cranberry flavonoids. The effect flavonoid extracts on the nanostructure of bulk SPC/GDO LC phases are lipid weight ratio-dependent. Flavonoids loaded into SPC/GDO-based formulations and LC phases retain their antioxidant properties. The self-assembled lipid liquid crystalline systems protect bioactive compounds from degradation. These facts are important for the community working in the field of self-assembly of lipid structures, food chemistry, and delivery vehicles of nutraceuticals

Synthesis, structural and luminescence properties of (La_1−xLn_x)₂Ti₂O₇ (Ln=lanthanides) solid solutions

International audienceno abstrac

Host-sensitized luminescence properties of KLa₅O₅(VO₄)₂:Eu³⁺ for solid-state lighting applications

International audienceno abstrac