Extraordinary Magnetic Properties of Ca1–xEuxS and Sr1–xEuxS Solid Solutions

The electron paramagnetic resonance (EPR) spectra and the stationary magnetic susceptibility are investigated for Ca_1–x Eu _x S and Sr_1–x Eu _x S solid solutions (0.00005 < x < 0.0032). The EPR spectrum of Eu²⁺ in both matrices contains a wide structureless line in addition to the narrow lines of the superfine structure characteristic of ions with high local symmetry. Because of the extraordinary temperature dependence of this line in CaS:Eu, it is associated with strongly interacting magnetic centers, namely, exchange-coupling pairs and chains or more complex clusters of magnetic ions. At the same time, the dependence of the stationary magnetic susceptibility in the temperature range 4.2–50 K has no peculiarities for CaS:Eu and SrS:Eu and obeys the Curie law.     

Formation of Eu<Superscript>2+</Superscript> and Eu<Superscript>3+</Superscript> centers in synthesis of CaF<Subscript>2</Subscript>:Eu luminophores

We have studied the effect of CaF₂:Eu luminophore synthesis methods on the charge state of europium. We have shown that Eu³⁺ predominates over Eu²⁺ in samples obtained by coprecipitation of europium with calcium fluoride, and the ratio Eu³⁺/Eu²⁺ grows as the total amount of europium increases. Partial charge conversion of the europium occurs during calcination of the samples, due to changes in the excess fluorine balance. We studied the luminescence, magnetic susceptibility, and EPR of the synthesized samples. We have shown that in a solid solution, europium forms large ordered clusters, determining both the luminescent and the magnetic properties of the material. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 6, pp. 773–779, November–December, 2007.     

Magnetic and EPR studies of the EuFe<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript> single crystal

Magnetic and electron paramagnetic resonance (EPR) properties of EuFe₃(BO₃)₄ single crystals have been studied over the temperature range of 300–4.2 K and in a magnetic field up to 5 T. The temperature, field and orientation dependences of susceptibility, magnetization and EPR spectra are presented. An antiferromagnetic ordering of the Fe subsystem occurs at about 37 K. The easy direction of magnetization perpendicular to the c axis is determined by magnetic measurements. Below 10 K, we observe an increase of susceptibility connected with the polarization of the Eu sublattice by an effective exchange field of the ordered Fe magnetic subsystem. In a magnetic field perpendicular to the c axis, we have observed an increase of magnetization at T < 10 K in the applied magnetic field, which can be attributed to the appearance of the magnetic moment induced by the magnetic field applied in the basal plane. According to EPR measurements, the distance between the maximum and minimum of derivative of absorption line of the Lorentz type is equal to 319 Gs. The anisotropy of g-factor and linewidth is due to the influence of crystalline field of trigonal symmetry. The peculiarities of temperature dependence of both intensity and linewidth are caused by the influence of excited states of europium ion (Eu³⁺). It is supposed that the difference between the g-factors from EPR and the magnetic measurements is caused by exchange interaction between rare earth and Fe subsystems via anomalous Zeeman effect.     

The Magnetic Response of Europium Implanted in Cerium and in Platinum as Investigated by the PAC-Method

The magnetic response of europium in γ-cerium and in platinum was studied by applying the perturbed angular correlation spectroscopy. The probe nuclei were ¹⁴⁷Eu(11/2⁻) and ¹⁴⁹Eu(11/2⁻). The response in γ-Ce was determined by the electronic S = J = 7/2 ground state of divalent Eu. In Pt, on the other hand, Eu is trivalent (J = 0 ground state). Here the magnetic contributions originate from Van Vleck terms of the whole multiplet system.     

Study on relationship of luminescence in CaS:Eu,Sm and dopants concentration

In order to study different characteristic luminescence of Eu²⁺ and Sm³⁺, delayed photoluminescence (DPL) and infrared stimulated luminescence (ISL) spectra of CaS doped with europium and samarium have been investigated. The influence of Eu and Sm concentration on luminescence of Eu²⁺ in photoluminescence (PL) and ISL was respectively studied. It was found that, at low doping levels, PL emission intensity of Eu²⁺ increased linearly with increment of Eu, while decreased linearly with increment of Sm. However, further increment of Eu and Sm in CaS:Eu,Sm could not increase either the luminescent centres of Eu²⁺ or electron trapping sites of Sm³⁺. Different local environment of Eu²⁺ and Sm³⁺ in the lattice position is thought to be the cause of all observed luminescence phenomena. Finally, the maximum emission in ISL was obtained at 1000 ppm europium and 750 ppm samarium.     

EPR and Magnetic Susceptibility of Na2O–CuO–P2O5 Glasses

Abstract

(50?x/2)Na₂O–xCuO–(50?x/2)P₂O₅ glasses (x=1, 5, 15, or 30 mol%) have been prepared and characterized by electron paramagnetic resonance (EPR) and magnetic susceptibility measurements. The shape of the Cu²⁺ EPR spectrum depends on the Cu content, and the corresponding computer simulations suggest that the Cu²⁺ ions occupy two different sites in these glasses: one of them is preponderant at low Cu content and the other is preponderant at high content, in which the Cu²⁺–Cu²⁺ interactions are more important. From EPR parameters, it was found that for the site at low content, the covalency of copper ion bonding with the surrounding ligands is appreciable. The magnetic susceptibility data appear to follow the Curie–Weiss law (χ=C/(T?θ_p)) with negative paramagnetic Curie temperature θ_p indicating antiferromagnetic interactions between Cu²⁺ ions that are more significant in the samples with high Cu content, in agreement with EPR results.     

A newly developed Fe-doped calcium sulfide nanoparticles with magnetic property for cancer hyperthermia

In this study, a magnetic iron-doped calcium sulfide (Fe–CaS) nanoparticle was newly developed and studied for the purpose of hyperthermia due to its promising magnetic property, adequate biodegradation rate, and relatively good biocompatibility. Fe–CaS nanoparticles were synthesized by a wet chemical co-precipitation process with heat treatment in a N₂ atmosphere, and were subsequently cooled in N₂ and exposed to air at a low temperature. The crystal structure of the Fe–CaS nanoparticles was similar to that of the CaS, which was identified by an X-ray diffractometer (XRD). The particle size was less than 40 nm based on a Debye–Scherrer equation and transmission electron microscope (TEM) examination. Magnetic properties obtained from the SQUID magnetometer demonstrated that the synthesized CaS was a diamagnetic property. Once the Fe ions were doped, the synthesized Fe–CaS converted into paramagnetism which showed no hysteresis loop. Having been heated above 600 °C in N₂, the Fe–CaS showed a promising magnetic property to produce enough energy to increase the temperature for hyperthermia. 10 mg/ml of the Fe–CaS was able to generate heat to elevate the media temperature over 42.5 °C within 6 min. The area of the hysteresis loop increased with the increasing of the treated temperature, especially at 800 °C for 1 h. This is because more Fe ions replaced Ca ions in the lattice at the higher heat treatment temperature. The heat production was also increasing with the increasing of heat treatment temperature, which resulted in an adequate specific absorption ratio (SAR) value, which was found to be 45.47 W/g at 37 °C under an alternative magnetic field of f = 750 KHz, H = 10 Oe. The in vitro biocompatibility test of the synthesized Fe–CaS nanoparticles examined by the LDH assay showed no cytotoxicity to 3T3 fibroblast. The result of in vitro cell hyperthermia shows that under magnetic field the Fe–CaS nanoparticles were able to generate heat and kill the CT-26 cancer cells significantly. We believe that the developed Fe–CaS nanoparticles have great potential as thermo-seeds for cancer hyperthermia in the near future.     

Superhyperfine structure of the EPR spectra of Ce<Superscript>3+</Superscript> ions in Li<Emphasis Type="Italic">R</Emphasis>F<Subscript>4</Subscript> (<Emphasis Type="Italic">R</Emphasis> = Y,Lu, Tm) double fluorides

The EPR spectra of Ce³⁺ impurity ions in LiYF₄, LiLuF₄, and LiTmF₄ double-fluoride single crystals have been investigated at a frequency of ∼9.3 GHz in the temperature range 5–25 K. The effective g factors of the ground Kramers doublet of the cerium ions in three crystals are close to each other (g _‖ = 2.737, g _⊥ = 1.475 for LiYF₄:Ce³⁺). A superhyperfine structure of the EPR spectrum of Ce³⁺ ions in the LiTmF₄ Van Vleck paramagnet has been observed in the external magnetic field B oriented along the crystallographic axis c (B ‖ c). The superhyperfine structure of the EPR soectra of the Ce³⁺ ions in the LiYF₄ and LiLuF₄ diamagnetic matrices is resolved for B ⊥ c. Possible factors responsible for this pronounced difference in the properties of the systems studied have been discussed.     

Enhancement of Europium Luminescence in Tetracycline–Europium Complexes in the Presence of Urea Hydrogen Peroxide

An increase in the europium emission band was observed, for the first time, with addition of urea hydrogen peroxide to the tetracycline–europium (Tc–Eu)solution. We have observed that the wavelength, the band width and the area of ⁵D₀→⁷F₂ europium transition change with the urea hydrogen peroxide concentration. We claim that the tetracycline–europium complexes can be used as probes of urea hydrogen peroxide concentration.     

The Co-luminescence Effect of Eu–Gd–Ofloxacin–SDBS System and its Analytical Application

A fluorescence enhancement phenomenon in the europium (Eu)–Ofloxacin (OF)–Sodium Dodecyl Benzene Sulfonate (SDBS) fluorescence system was observed when Gd³⁺ was added. The fluorescence intensity of the systems was measured (λ _ex/λ _em = 280/612 nm) at pH 7.8. Under optimum conditions, a linear relationship between the enhanced fluorescence intensity and the Eu³⁺ concentration in the range of 5.0 × 10⁻¹⁰ ∼ 2.0 × 10⁻⁷ mol·L⁻¹ was observed. The detection limit of Eu³⁺ was 1.46 × 10⁻¹⁰ mol·L⁻¹ (S/N = 3). This method was used for the determination of trace amounts of europium in synthetic rare earth samples with satisfactory results. In addition, the interaction mechanism is also studied.     

EPR of Fe3+ ion and symmetry of [AIF5·H2O]2? complex ion in (NH4)2AIF5·H2O single crystals

We used the spin-Hamiltonian method for the analysis of the electron paramagnetic resonance (EPR) spectrum of Fe³⁺ as a probe ion in (NH₄)₂AlF₅·H₂O single crystalline basic material. The theoretical expressions for the magnetic field (at which the fine structure transition lines appear) versus the angle between the magnetic field and the axis of symmetry of the magnetic complex are also given. These values were calculated by applying the perturbation theory to the second-order terms. From the experimental results (at 300 K and 9.21 GHz), the spin-Hamiltonian parameters were deduced:D=(668±10)·10⁻⁴ T,E=(−56±10)·10⁻⁴ T,a=(−54±10)·10⁻⁴ T,F=(30±10)·10⁻⁴ T. An isotropic superhyperfine structure was evidenced for the five fluorine ions. The obtained EPR data were used to determine the local symmetry of the Al³⁺ ion. A good agreement with X-ray diffraction measurements was found.     

Electrical conductivity and luminescence of metal-organic nanocomposites

We presented the results of experimental study of electrical and luminescence properties of planar nanocomposites based on gold island films and layers of efficient organic luminophores — aluminum (III) 8-hydroxyquinolinate (Alq₃) and europium β-diketonates [Eu(DBM)₃ bath, Eu(DBM)₃ phen, and Eu(DBM)₃]. The mechanisms of electroluminescence of such hybrid systems are discussed and the processes of luminescence excitation in the organic component of nanocomposites are considered in detail. It is shown that the spectral characteristics of europium β-diketonates are controlled by the Eu³⁺ ion fluorescence. The proposed mechanisms of nanocomposite electroluminescence are confirmed by the results of measurements of cathodoluminescence spectra of organic luminophores.     

Ferromagnetism in Cu-doped ZnSe semiconducting quantum dots

The projection of integrating optical, magnetic and electronic functionalities into a single material have aggravated passionate attention in mounting wide band gap diluted magnetic semiconductor (DMS) in the midst of room temperature ferromagnetism. We report the evidence of ferromagnetism in Cu-doped ZnSe quantum dots (QDs) below room temperature, grown from a single source precursor by lyothermal method with the sizes of approximately 3.2–5.14 nm. QDs mainly exhibit paramagnetic behavior between 80 and 300 K, with a weak ferromagnetic/anti-ferromagnetic exchange at lower temperature as observed by superconducting quantum interference device (SQUID) magnetometer. From the Curie–Weiss behavior of the susceptibility, Curie temperature (T _c) of Cu-doped ZnSe sample has been evaluated. From EPR, we obtain the Lande-g factor in the Zeeman interaction term as 2.060. Photoluminescence and EPR measurements support and confirm the view that Cu²⁺ substitutes for Zn²⁺ in Cu-doped ZnSe quantum dots.     

1H NMR Spectral Simplification with Achiral and Chiral Lanthanide Shift Reagents. Mexiletine

The 60 MHz ¹H NMR spectra of mexiletine, 1-(2,6-dimethylphenoxy)-2-propanamine, 1, have been studied at 28° in CDCl₃ solution with the achiral reagent, tris(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionato) europium(III), 2, Eu(FOD)₃, and the chiral reagents tris[3-(trifluoromethylhydroxymethylene)-d-camphorato]europium(III), 3, Eu(FACAM)₃, and tris[3-(heptafluoropropylhydroxymethylene)-d-camphorato]europium(III), 4, Eu(HFC)₃. Substantial lanthanide-induced shifts were seen for the proton signals of 1 with each reagent. Appreciable enantiomeric shift differences were seen for both methyl signals and for each of the CH₂CH proton signals using 3 and 4 that should permit direct determinations of enantiomeric excess for samples of 1. A predominant conformation for 1 is suggested based on observed splittings of the CH₂ proton signals and their relative lanthanide-induced shifts.     

A europium(III) organic ternary complex applied in fabrication of?near UV-based white light-emitting diodes

A β-diketone, 2-acetylfluorene-4,4,4-trifluorobutane-1,3-dione (HAFTFBD), and its three europium(III) complexes, Eu(AFTFBD)₃⋅2H₂O, Eu(AFTFBD)₃(TPPO)₂ and Eu(AFTFBD)₃phen, were designed and synthesized, where TPPO was triphenylphosphine oxide and phen was 1,10-phenanthroline. The complexes were characterized by IR, UV-visible, photoluminescence (PL) spectroscopy and thermogravimetric analysis (TGA). The results show that the Eu(III) complexes exhibit a high thermal stability,and wide and strong excitation bands when monitored at 613 nm. Excited by ∼395 nm near UV light, the complexes emitted strong and characteristic red light due to f–f transitions of the central Eu³⁺ ion, and no emission from the ligands was found. The photoluminescence mechanism of the europium(III) complexes was investigated and proposed as a ligand-sensitized luminescence process. Among the three europium(III) complexes, Eu(AFTFBD)₃phen exhibits the highest thermal stability and the most excellent photoluminescence properties. A bright red light-emitting diode was fabricated by coating the Eu(AFTFBD)₃phen complex onto an ∼395 nm-emitting InGaN chip, and the LED showed appropriate CIE chromaticity coordinates (x=0.66, y=0.33). A white LED with CIE chromaticity coordinates (x=0.32, y=0.32) was prepared with Eu(AFTFBD)₃phen as red phosphor, indicating that Eu(AFTFBD)₃phen can be applied as a red component for fabrication of near ultraviolet-based white light-emitting diodes.     

Magnetic and electrical properties of Mg1−x CuxO solid solutions and magnetic shielding in Cu-Mg1−x CuxO structures

Mg_1−x Cu_xO solid solutions having an NaCl structure with 0⩽x⩽0.20 are synthesized and Cu-Mg_1−x Cu_xO structures are prepared for superconductivity studies. The magnetic susceptibility χ, electron paramagnetic resonance (EPR), and electrical conductivity of the solid solutions are studied at temperatures of 5–550 K. It is shown that χ ⁻¹(T) obeys the Curie-Weiss law with a paramagnetic Curie temperature Θ close to zero and an effective magnetic moment μ _eff=1.9 μ _B, close to the 1.73 μ _B of a Cu²⁺ ion with spin S=1/2. The width ΔH of the EPR line depends weakly on temperature and increases as x is raised. The volume narrowing of the EPR linewidth ΔH is used to estimate the exchange interaction parameter, 3×10⁻⁴ eV. The g-factor is close to 2 and is temperature independent. The electrical conductivity of Mg_1−x Cu_xO at T=300 K is ≈10⁻¹¹–10⁻¹² Ω⁻¹ cm⁻¹ for x=0 and increases to 10⁻⁵–10⁻⁶ Ω⁻¹ cm⁻¹ for x=0.15–0.20. The conductivity is p-type. Magnetic shielding is observed in Cu-Mg_1−x Cu_xO structures with x=0.15 and 0.20. The possible connection of this phenomenon with interference superconductivity in the contact layer of the structure is discussed. Fiz. Tverd. Tela (St. Petersburg) 41, 293–296 (February 1999)     

Europium-sensitized Chemiluminescence of System Tetracycline–H<Subscript>2</Subscript>O<Subscript>2</Subscript>–Fe(II)/(III) and Its Application to the Determination of Tetracycline

Chemiluminescence (CL) of the reaction system tetracycline–H₂O₂–Fe(II)/(III)–Eu(III) was used for the determination of tetracycline hydrochloride in water, pharmaceutical preparations, and honey. The CL spectrum registered for this system shows emission bands typical of Eu(III) ions, with a maximum at λ ∼ 600 nm, corresponding to the electronic transitions of ⁵D₀ → ⁷F₁ and ⁵D₀ → ⁷F₂. A strong chemiluminescence intensity characteristic of europium(III) ions in the system tetracycline–H₂O₂–Fe(II)/(III)–Eu(III), as contrasted to the emission of the system tetracycline–H₂O₂–Fe(II)/(III) without Eu(III), proves that the Eu(III) ion plays the role of a chemiluminescence sensitizer, accompanying tetracycline oxidation in the Fenton system (H₂O₂–Fe(II)/(III)). A linear dependence was observed for the integrated CL light intensity on the tetracycline concentration in the range of 2 × 10⁻⁷ to 3 × 10⁻⁵ mol l⁻¹ with the detection limit of 5 × 10⁻⁸ mol l⁻¹ in aqueous solution.     

Magnetic resonance of intrinsic defects in the spin-Peierls magnet CuGeO3

Magnetic resonance in pure single-crystal CuGeO₃ at frequencies 9–75 GHz in the temperature range 1.2–25 K is investigated. Splitting of the magnetic-resonance line into several spectral components is observed at temperatures below 5 K, where spin-Peierls dimerization suppresses the magnetic susceptibility and the ESR signal intensity. Analysis of the magnetic resonance spectra over a wide frequency range with different directions of the magnetic field at different temperatures makes it possible to identify among these components the ESR signals due to defects, having effective spin S=1/2 and spin S=1, in the spin-Peierls phase. The g factor corresponding to these ESR signals is the same and close to the value characteristic for the ion Cu²⁺. Another magnetic-resonance line is characterized by a strongly anisotropic g factor and an increase (at a threshold in the excitation power) in the susceptibility both at resonance and in the line wings. These signals are tentatively attributed to two possible types of planar defects arising on the walls of domains of the spin-Peierls state with different values of the dimerization phase. Zh. éksp. Teor. Fiz. 114, 1876–1896 (November 1998)     

1H NMR Spectral Simplification with Achiral and Chiral Lanthanide Shift Reagents. Methastyridone, 2,2-Dimethyl-5-(2-Phenylethenyl)-4-Oxazolidinone

Abstract

The 60 MHz ¹H NMR spectra of methastyridone, 2,2-dimethyl-5-(2-phenylethenyl)-4-oxazolidinone, 1, have been studied at 28° in CDCl₃ solution with the achiral reagent tris(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionato)europium(III), 2, Eu(FOD)₃, and the chiral reagent tris[3-(heptafluoropropylhydroxy-methylene)-d?camphorato]europium(III), 3, Eu(HFC)₃.