Increasing Eu Concentration Research Articles

Influence of Eu substitution on structural, magnetic, optical and dielectric properties of BiFeO3 multiferroic ceramics

Eu substituted BiFeO3 (Bi1−xEuxFeO3; x=0–0.15) polycrystalline ceramics were synthesized by a solid state reaction method. Rietveld refinement of X-ray diffraction patterns reveals that samples crystallize in R3c structure for x≤0.10 and (R3c+Pn21a) phases coexist for x≥0.12–0.15. The magnetic measurements show weak ferromagnetic nature of Eu substituted BiFeO3 samples due to ferromagnetic coupling between Eu3+ and Fe3+ ions. The remnant magnetization is found to increase from 0.0003emu/g for x=0.00 to 0.087emu/g for x=0.15. The gradual change in line shape of electron spin resonance spectra has been attributed to local distortion induced by Eu substitution. UV–visible absorption spectra in the spectral range 1.12–3.5eV were dominated by two charge transfer transitions and two doubly degenerate d–d transitions. The optical band gap is found to decrease from 2.25 to 2.16eV with increasing Eu concentration. Improved dielectric properties with enhancement in frequency independent region of dielectric constant and loss have been observed.

Solvothermal synthesis, characterization and photoluminescence studies of ZnS:Eu nanocrystals

Europium doped zinc sulfide nanocrystals (ZnS:Eu) are prepared by solvothermal method. Crystallite size and lattice constant of the prepared samples are calculated from the X-ray diffraction patterns. The as-prepared samples are found to be a mixture of complex chemical groups. Heat treatment of the samples at 300°C resulted in ZnS:Eu state. The crystal structure is not affected by the increase in the concentration of Eu from 1mol% to 5mol%. Fourier Transform Infrared Spectroscopy (FTIR) studies showed that characteristic absorption bands of hydroxyl groups and the acetate bands increased with increase in Eu concentration. The morphological results studied using Scanning Electron Microscopy (SEM) indicate agglomeration of nanoparticles and a marginal increase in the particle size. Photoluminescence (PL) spectra of the samples showed a prominent emission band peaked at ∼400nm besides three weak ones at ∼422, 485 and 530nm. The PL intensity increased with increase in Eu concentration.

Structure, optical and magnetic properties of Bi 1−x Eu x FeO 3 films fabricated by pulsed laser deposition

Abstract Multiferroic Bi 1− x Eu x FeO 3 (BEFO x , x = 0, 0.03, 0.05, 0.07, 0.10) films were grown on (1 0 0) SrTiO 3 substrates by pulsed laser deposition. X-ray diffraction analysis indicates the strong ( h 0 0) peaks, and no impurity phases are observed. Atomic force microscopy shows the root mean square roughness of the films is less than 0.87 nm, which indicates the BEFO x films are smooth and uniform. Transmittance spectra demonstrate that the optical band gap of the BEFO x films decreases with increasing Eu content. The saturation magnetization M s of the BEFO x films is significantly enhanced with increasing Eu content, which provides potential applications in magnetoelectric memory devices and data storage media.

Europium incorporated barium titanate thin films for optical applications

BaTiO3:Eu (BT:Eu) thin films were deposited onto quartz substrates by RF magnetron sputtering. The effect on structural, morphological, optical and photoluminescence (PL) properties in the films with different Eu concentrations (0–5 wt%) were investigated. The X-ray diffraction (XRD) pattern of the undoped BT thin film revealed a tetragonal (T) phase with orientations along (101) plane. From XRD pattern, the crystallinity of the films increased with increase in Eu concentration. The SEM images revealed that the films exhibited tetragonal shape, crack free and good adherence to the substrate. Atomic force microscopy studies showed an increase of grain growth with doping concentration. The rms roughness value increased with increase in Eu concentration and the film surface revealed positive skewness and high value of kurtosis which make them suitable for tribological applications. X-ray photoelectron spectroscopy revealed the presence of barium, titanium, europium and oxygen in BT:Eu film. An average transmittance of >80 % (in visible region) was observed for all the films. Optical band gap of Eu doped BT films decreased from 3.86 to 3.53 eV. Such films with optical properties such as high transparency, decrease in band gap and high refractive index are suitable for optoelectronic applications. PL properties showed a sharp line at 625 nm and a broad line at 552 nm due to europium (Eu3+) transitions. PL phenomena were observed, owing to the electronic structure of Eu3+ ions as well as BT nanocrystallites in the films. The sharp and intense red luminescence is useful for photoelectric devices and optical communications.

Photoluminescence and radioluminescence study of NaMgF3:Eu nanoparticles

Photoluminescence (PL) and radioluminescence (RL) measurements were made on small (∼25 nm) NaMgF3 nanoparticles doped with Eu concentrations ranging from 0.1% to 5%. We find that they contained Eu3+, Eu2+, and an additional unidentified defect with a broad PL emission ∼470 nm. Similar to previous measurements on larger (57 nm–77 nm) NaMgF3:Eu nanoparticles with 1% Eu and 5% Eu, we find that the PL lifetime decreases with increasing Eu concentration that can be attributed to Eu energy transfer to non-radiative recombination sites. However, there is no change in the fraction of Eu3+ distorted sites. The ∼470 nm PL defect peak was also reported for larger nanoparticles, which suggests that this peak arises from similar unidentified point defects. However, the activated non-radiative decay for the small nanoparticles has a significantly lower activation energy. The Eu3+ RL decreases by only 2.3% at 10 kGy for low Eu concentrations.

Magnetic and transport properties of layered perovskite manganites (La1-xEu x)4/3Sr5/3Mn2O7(x=0, 0.15)

The samples (La1-xEux)4/3Sr5/3Mn2O7 (x=0, 0.15) were prepared by the traditional solid-state reaction, and their magnetic and electrical properties were investigated. The magnetzation measurement reveals that as temperature lowers, all the samples undergo a complex magnetic transition process: they transform from the two-dimensional short-range ferromagnetic order at T* into the three-dimensional long-range ferromagnetic state at TC. With the increase of Eu doping, T* and TC are both reduced, and the sample (La0.85Eu0.15)4/3Sr5/3Mn2O7 exhibits spin-glass-like behaviour in a low temperature region. Electrical property measurements show that with the increase of Eu concentration, resistivity sharply increases, the metal-insulator transition temperature decreases and the magnetoresistance peak increases. These effects are attributed to the decrease of the average ionic radius diminution and the lattice distortion due to the substitution of the smaller Eu3+ ions for La3+ ions. In addition, the small-sized Eu3+ ion preferentially occupies the R site in the rock-salt layer, then the distributions of La3+, Sr3+, Eu3+ ions in the sample (La0.85Eu0.15)4/3Sr5/3Mn2O7 should be more orderly, so there is only one peak in the ρ-T curve of the sample with x=0.15.

Eu-doping induced improvement on the second harmonic generation of ZnO Nanowires

ABSTRACTWe report the Eu doping induced improvement on the second harmonic generation (SHG) of ZnO nanowires and correlates with the structural modification and corresponding linear absorption. A non-monotonic enhancement in the SHG emission is observed with the increase of Eu concentration. To understand the underlying mechanism, the effective second order non–linear coefficient (deff) is calculated from the theoretical fitting with considering the absorption effect. The highest deff (19.09±0.11 pm/V) is obtained for the 1 at.% Eu doped ZnO nanowires, which is several times larger than the standard SHG material β-BaB2O4 (BBO). Dependence of the deff with the Eu doping, structural modification and absorption magnitude are systematically discussed.

A positron annihilation spectroscopic investigation of europium-doped cerium oxide nanoparticles

Doping in ceria (CeO2) nanoparticles with europium (Eu) of varying concentrations (0, 0.1, 0.5, …, 50 atom%) is studied using complementary experimental techniques and novel observations were made during the investigation. The immediate observable effect was a distinct reduction in particle sizes with increasing Eu concentration attributed to the relaxation of strain introduced due to the replacement of Ce(4+) ions by Eu(3+) ions of larger radius. However, this general trend was reversed in the doping concentration range of 0.1-1 atom% due to the reduction of Ce(4+) to Ce(3+) and the formation of anion vacancies. Quantum confinement effects became evident with the increase of band gap energy when the particle sizes reduced below 7-8 nm. Positron annihilation studies indicated the presence of vacancy type defects in the form of vacancy clusters within the nanoparticles. Some positron annihilation was also seen on the surface of crystallites as a result of diffusion of thermalized positrons before annihilation. Coincidence Doppler broadening measurements indicated the annihilation of positrons with electrons of different species of atoms and the characteristic S-W plot showed a kink-like feature at the particle sizes where quantum confinement effects began.

Effects of Eu3+ Doping on Characteristics of (Bi3.25Nd0.75)Ti3O12 Nanoplates

a- and b-axis-oriented (Bi3.25Nd0.75 - xEux)Ti3O12 (BNEuT, x = 0–0.75) films of 3.0 µm thickness were fabricated on conductive Nb:TiO2(101) substrates containing 0.79 mass % Nb by high-temperature sputtering at 650 °C, and their structural and ferroelectric characteristics were investigated. All the films had a mostly single-phase orthorhombic structure, with high degrees of a- and b-axis orientations of 99.0–99.8%. The lattice parameters (a-, b-, and c-axis lengths) and the calculated orthorhombic lattice distortion decreased monotonically with increasing Eu content. The microstructure of BNEuT films with x = 0–0.50 was nanoplate-like, whereas that of films with x≥0.60 was significantly more bulk-like. The real room-temperature remanent polarization (2Pr*), taking the porosity between the nanoplates into account, had a maximum value of 2Pr* = 87 µC/cm2 at x = 0.10, which was approximately 1.3 times larger than that (65 µC/cm2) of the nondoped BNT film. It is shown that lattice distortion caused by rotation of octahedra in the a–b plane due to the Eu substitution plays a significant role in the improvement of ferroelectricity.

Fabrication and Characterization of Calcium Silicate Phosphors - Ca<sub>2</sub>SiO<sub>4</sub> and Ca<sub>2</sub>MgSi<sub>2</sub>O<sub>7</sub> -

Calcium silicate phosphors, Ca2-xSiO4(CS):Eu3+x, CS:Eu2+x and Ca2-y-zMgSi2O7 (CMS):Eu2+y,Dy3+z were prepared by the solid state reaction. The phases in CS:Eu3+ system were β- and αL’ -types. The fluorescent color under a black-light irradiation was red and the emission spectrum consisted of 590nm(αL’), 615nm(β) and 625nm(αL’) peaks. The emission intensity took a maximum value at x=0.2. The addition of B3+ accelerated the solid solution of Eu3+. The phase in CS:Eu2+ system was β-type only. The fluorescent color was yellow-green(520nm). The emission intensity took a maximum value at x=0.01. The CMS product showed the akermanite phase. The lattice constants of CMS:Eu2+ increased with increasing Eu content, but those became constant at y>0.05. The fluorescent color of CMS:Eu2+ was yellow-green and the emission intensity took a maximum value at y=0.03. In the case of CMS:Eu2+0.03,Dy3+z, the fluorescent color and the afterglow color were same, yellow-green. The emission intensity took a maximum value at z=0.06. The longest afterglow time, 23min., was obtained at z=0.09. The trap depth were 0.64-0.69 eV.

Role of intervalley scattering in the radiative recombination in Pb1 − x Eu x Te alloys (0 ≤ x ≤ 1)

Measurements of the photoluminescence from epitaxial layers of Pb1 − xEuxTe alloys with 0 ≤ x ≤ 0.32 are carried out. It is found that the luminescence intensity decreases with increasing Eu content and, already for x as low as about 0.1, drops by more than one order of magnitude. No luminescence is observed for 0.2 0.85, optical transitions also take place with the participation of the X valley; in this case, the emission is governed by the formation of magnetic polarons. The temperature dependences of the band gap are determined for 0 ≤ x ≤ 0.11. These dependences have a wide linear region characterized by a positive dEg/dT coefficient, which decreases with the Eu content to become negative in pure EuTe.

Effect of Eu Doping on Magnetocaloric Effect in Sm0.6Sr0.4MnO3

The electrical, magnetic and magnetocaloric properties of Sm0.6−xEuxSr0.4MnO3 were investigated for x = 0, 0.2 and 0.4. The Curie temperature decreases from 114 K to 62 K and Metal-Insulator transition temperature also decreases with increasing Eu content. A low temperature maximum is found within the long range ferromagnetic order in field-cooled magnetization of x = 0 which shifts down in temperature with increasing Eu doping and goes below the measured temperature range for x = 0.4. The value of maximum magnetic entropy change increases with increasing x (∼ 8 J/kg.K for ΔH = 5 T) with a calculated net Refrigerant Capacity in the range of 270 J/kg. Thus, Eu doping proves to be an efficient method to tune the Curie temperature of the material in order to obtain a significant refrigerant capacity at desired temperatures.

Structure and multiferroic properties of Eu-substituted BiFeO3 ceramics

Polycrystalline Bi1−xEuxFeO3 (x=0.00–0.25) ceramics were synthesized by the solid state reaction method with the rapid liquid phase sintering process. The effects of Eu substitution on the structure, and ferroelectric and magnetic properties of BiFeO3 ceramics were investigated. X-ray diffraction measurements reveal that the structure of BiFeO3 was changed from rhombohedral to orthorhombic and the impurity phases were decreased both due to Eu substitution. Raman spectra results also confirm that a structure transition occurs in the Eu concentration range of 0.15–0.20. The SEM investigation has suggested that the Eu substitution hinders the grain growth. Vibrating sample magnetometer measurements indicate ferromagnetism in Eu-substituted BiFeO3 ceramics. It is found that the room temperature magnetic moment increases with increasing Eu concentration due to the suppressed or broken cycloid spin structure. Ferroelectric measurements show that Eu substitution enhances the polarization due to the significant decrease of the electric leakage of the samples. Therefore, the Eu-substituted BiFeO3, or more complicated substituted BiFeO3 based on Eu substitution, will have great potential for many practical applications.

Study of electrical transport properties of Eu+3substituted MnZn-ferrites synthesized by co-precipitation technique

Eu substituted MnZn-ferrites with nominal composition Mn0.78Zn0.22Eux Fe(2−x)O4 (x=0.0, 0.02, 0.04, 0.06, 0.08 and 0.10) were prepared by co-precipitation technique. The effect of Europium substitution on electrical transport properties of Mn–Zn ferrites is reported. XRD analysis reveals fcc phase in all the samples along with few traces of second phase. The lattice constant shows decreasing trend with the substitution of Eu due to partial solubility of Eu-ions in the lattice. Room temperature resistivity both at 10 and 20V shows on average an increasing trend. This increase in resistivity is attributed to the unavailability of Fe+3 ions in the lattice due to Eu-substitution. The dc resistivity decreases with temperature for all the samples at 10V and 20V indicating the semiconducting behavior of these samples. Room temperature dc resistivity and activation energies show similar trend both at 10V and 20V indicating that the samples with high resistivity have high activation energies and vice versa. The dielectric constant (ε′), complex dielectric constant (ε″) and loss tangent of these samples decreased with the increase of Eu-concentration, following the Maxwell–Weigner model.

Preparation, Structural Characterization, and Enhanced Electrical Conductivity of Pyrochlore‐type (Sm1–xEux)2Zr2O7 Ceramics

Abstract(Sm1–xEux)2Zr2O7 (0 ≤ x ≤ 1.0) samples are prepared by solid state reaction method using Sm2O3, Eu2O3, and ZrO2 as starting materials. The phase composition and microstructure of (Sm1–xEux)2Zr2O7 ceramics are investigated by X‐ray diffraction (XRD), scanning electron microscopy, high‐resolution transmission electron microscopy (HRTEM) coupled with selected area electron diffraction and Raman spectroscopy. XRD and TEM show that all the samples exhibit a single pyrochlore‐type structure. HRTEM observation indicates that the whole grain interior of Sm2Zr2O7 ceramic is a perfect crystal free of any dislocation. Raman spectroscopy reveals that the degree of structural disorder of (Sm1–xEux)2Zr2O7 ceramics increases gradually with increasing Eu content. The electrical conductivity of (Sm1–xEux)2Zr2O7 ceramics is investigated by impedance spectroscopy in the air and hydrogen atmospheres, respectively. The electrical conductivity of (Sm1–xEux)2Zr2O7 ceramics increases with increasing Eu content at identical temperature levels. Both the activation energy Eg and the pre‐exponential factor σ0g for the grain conductivity gradually increase with increasing Eu content. As the ionic conductivity shows no obvious change in both air and hydrogen atmospheres, the conduction of (Sm1–xEux)2Zr2O7 is purely ionic with negligible electronic conduction.

Correlation Between Charge, Spin and Lattice in La–Eu–Sr Manganites

To understand the structural, electrical, magnetic, elastic and anelastic properties of La0.67−xEuxSr0.33MnO3 (0.30≤x≤0.39) manganites, a series of samples was prepared by citrate gel route. X-ray diffraction studies along with Rietveld analysis indicate the samples crystallize in single phase with Pnma space group. Studies on the variations of magnetization with temperature indicate that the Curie transition temperature (TC) decreases with increasing Eu content. Furthermore, Eu substitution is found to increase the electrical resistivity and significantly enhances the colossal magnetoresistance effect, while it is found to decrease the characteristic metal–insulator transition temperature (TP). On analyzing the electrical resistivity data, it has been concluded that the resistivity below TP can be explained based on electron–electron, electron–phonon and two magnon scattering processes, while that above TP, the adiabatic small polaron model is found to explain the observed behavior. Finally, the longitudinal modulus (L) and internal friction (Q−1) have been measured and a dramatic change in L (T) is observed at TC, accompanied by a sharp peak in Q−1 (T). Simultaneous occurrence of magnetic, transport and lattice anomalous behavior at TC indicate the presence of strong electron–phonon and spin–phonon interactions in these manganites.

Concentration quenching in Eu-doped ZnO grown by sputtering-assisted metalorganic chemical vapor deposition

The dependence of Eu3+ photoluminescence (PL) properties on Eu concentration was studied in Eu-doped ZnO (ZnO:Eu) thin films grown by sputtering-assisted metalorganic chemical vapor deposition (SA-MOCVD). The ZnO:Eu showed band-edge PL from ZnO and red emission lines due to the intra-4f transitions in Eu3+ ions at room temperature (RT). The intensities of band-edge and Eu3+ PL decreased with the increasing Eu concentration. In the temperature dependence of Eu3+ PL, the ZnO:Eu with high Eu concentration showed large thermal quenching of the PL intensity. In addition, the lifetimes of Eu3+ PL became short at high Eu concentration. The concentration quenching mechanism of Eu3+ PL using a model based on non-radiative recombination processes in ZnO and Eu3+ ions was presented.

Synthesis and photoluminescence of Eu, Mg-alon phosphors by carbothermal reduction

Eu 2+–Mg 2+ co-doped alon phosphors were successfully prepared by carbothermal reaction at 1600 °C for 2 h and their structure and photoluminescence properties were studied. The lattice parameter increased with increasing Eu concentration, indicating the incorporation of Eu into alon crystal lattice. The pure alon phase was obtained when Eu concentration is below 0.2%. Compared with solid state reaction process, this method lead to less amounts of secondary phase, larger amounts of Eu 2+ against Eu 3+, smaller particle size, narrower particle size distribution and stronger luminescence intensity. The absolute emission intensity of obtained phosphor reached 82% relative to that of famous BAM: Eu 2+ phosphor. The emission could be tuned widely from blue to green by varying carbon content.

Effects of Europium Substitution on the Microstructure and Electric Properties of Bismuth Ferrite Ceramics

Bi1−xEuxFeO3 (x=0.00–0.15) ceramics were synthesized by solid state reaction method with rapid liquid phase sintering process at different europium content and the microstructure and electrical properties of the samples were investigated. X-ray diffraction (XRD) studies show that europium substitution has changed the structure of BiFeO3 from rhombohedral R3c to orthorhombic Pnma and decreased the impurity phase. Raman spectra results also conform that a structure transition occurs at about x=0.20, and indicate that the Eu substitution at Bi site can obviously affect the Bi–O bond. Impedance analyzer measurements show that both dielectric constant and dielectric loss are strongly dependent on the Eu content. The dielectric constant of the Bi1−xEuxFeO3 increases with increasing Eu content from 0.00 to 0.20, then decreases with increasing Eu content from 0.20 to 0.30. The dielectric constant measured at 100 Hz is 542.0 for the x=0.20 sample, which is about 8.5 times as big as that for unsubsitituted BiFeO3. The dielectric loss can be effectively decreased by the substitution of Eu for Bi. In addition, the leakage current measurements show that the substitution of Eu can effectively reduce the leakage current density of BiFeO3.

Superconducting state of very thin Pd films deposited on a diluted insulating EuxSr1−xS ferromagnet

The electronic transport in very thin Pd films deposited on insulating Eu${}_{x}$Sr${}_{1\ensuremath{-}x}$S ($0\ensuremath{\leqslant}x\ensuremath{\leqslant}1$) is investigated. The temperature dependent resistance $R(T)$ of films with ${d}_{\mathrm{Pd}}\ensuremath{\geqslant}14$ nm shows metallic behavior and a logarithmic increase toward low temperatures characteristic of (anti-)localization and electron-electron interaction effects also observed for Pd films on Si(111). Films with ${d}_{\mathrm{Pd}}=7$ nm are superconducting below a transition temperature ${T}_{c}$ which decreases with increasing Eu concentration from ${T}_{c}=0.9$ K for $x=0$ to ${T}_{c}l50$ mK for $x=1$. The origin of superconductivity in the thin Pd films is presumably due to the formation of an interfacial Pd-S alloy and/or to a charge transfer at the Pd/Eu${}_{x}$Sr${}_{1\ensuremath{-}x}$S interface. The decrease of ${T}_{c}$ vs $x$ is attributed to the magnetic pair breaking of the ferromagnetic Eu${}_{x}$Sr${}_{1\ensuremath{-}x}$S underneath. The $R(T)$ behavior of films with ${d}_{\mathrm{Pd}}\ensuremath{\geqslant}10$ nm suggests that these are not superconducting or have a strongly reduced ${T}_{c}$ presumably due to the proximity effect of the nonsuperconducting S-free upper part of the Pd film.