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We report the results of measurements of thermal conductivity coefficient dependence on temperature of single crystals of SrIr4In2Ge4 and EuIr4In2Ge4. The measurements were carried out over the temperature range of ∼5–300 K. The EuIr4In2Ge4 crystal, unlike its strontium analog SrIr4In2Ge4, shows an amazing anisotropy: At low temperatures, it displays significantly smaller thermal conductivity in the ab plane than in the direction of c axis, while at the high ones the thermal conductivity in the direction perpendicular to the c axis increases well above that of in the c axis. The observed phenomena may be a result of the interaction of phonons with 1D chains of short-range ordered magnetic moment of europium atoms and the exchange energy between the chains in the paramagnetic phase of EuIr4In2Ge4. [ABSTRACT FROM AUTHOR]

Transition-metal and rare-earth borides are of considerable interest due to their electronic, mechanical, and magnetic properties as well as their structural stability under extreme conditions. Here, we report on a series of high-pressure Raman and x-ray diffraction experiments on the cubic rare-earth hexaboride EuB6 to an ultrahigh pressure of 187 GPa in a diamond anvil cell. In EuB6, divalent europium ions occupy the corners of the cubic structure, which encloses a rigid boron-bonded cage. So far, no structural phase transitions have been reported, while the nanoindentation studies indicate amorphization in nanoscale shear bands during plastic deformation. Our x-ray diffraction studies have revealed that the ambient cubic phase of EuB6 shows broadening and splitting of diffraction peaks starting at 72 GPa and the broadening continuing to 187 GPa. The high-pressure phase is recovered on decompression, and the Raman spectroscopy of the recovered sample from 187 GPa shows a downward frequency shift and broadening of T2g, Eg, and A1g modes of boron octahedron. The density functional theory simulations of EuB6 at 100 GPa have identified five possible lowest energy crystal structures. The experimental x-ray diffraction data at high pressures is compared with the theoretical predictions and the role of structural distortions induced by shear stresses is also discussed. [ABSTRACT FROM AUTHOR]

Polyvinylidene difluoride trifluoroethylene (PVDF-TrFE) has received widespread application in flexible electronics and biomedical devices but is limited in its sensing modalities to piezoelectricity and pyroelectricity. The addition of optically or magnetically active nanoparticles could provide additional sensing modalities in the same element, which could drive miniaturization of such sensors. Europium barium titanate (EBTO) is one such optically active nanoparticle that could add functionality to such a nanocomposite. In this work, multifunctional nanocomposites of PVDF-TrFE and EBTO are successfully synthesized and characterized for their material and electronic properties. The nanocomposite in this work is the first known multifunctional nanocomposite with PVDF-TrFE and a fluorescent nanoparticle. [ABSTRACT FROM AUTHOR]

Distributions of Eu2+ and Eu3+ do affect the optical properties. However, the substitution of the activator ions hardly perturbed the crystal structure of the host lattice. Without the differences in crystal structure, it is not trivial to develop an effective descriptor to investigate stoichiometry-dependent mechanism to explore the effects of Eu species on valence states. In this study, through x-ray nanodiffraction, x-ray fluorescence, x-ray absorption near edge structure, and x-ray excited optical luminescence, we mapped the valence state distributions of Eu species to calculate the local mixing enthalpy and entropy. The calculated thermodynamics parameters show good agreement with the optical properties. We found that Eu2+ of Eu-doped BaAl2O4 predominantly existed in a divalent state, which results in segregation phenomena of local Eu2+ and Eu3+ ions. [ABSTRACT FROM AUTHOR]

The images for Figs. 5 and 6 have been inadvertently switched.[1] The image for Fig. 5 is in Fig. 6 and vice versa. Figures 5 and 6 should have been shown as below. The authors apologize for any inconvenience this mistake may have caused.Graph: FIG. 5. Ferroelecric hysteresis of PVDF-TrFE/EBTO nanocomposites.Graph: FIG. 6. (a) Real permittivity of PVDF-TrFE/EBTO nanocomposites. (b) Imaginary permittivity of PVDF-TrFE/EBTO nanocomposites.By Christine K. McGinn; Nasim Farahmand; Stephen O'Brien and Ioannis KymissisReported by Author; Author; Author; Author [Extracted from the article]

Structure and energetics of rare-earth (RE) defects and luminescence of RE and related defects in zincblende zinc sulfide (ZnS) are investigated using hybrid density-functional defect calculations. We find that europium (Eu) is stable predominantly as the divalent Eu 2 + ion in bulk ZnS. The trivalent Eu 3 + ion is structurally and electronically stable but energetically unfavorable compared to Eu 2 + due to the presence of low-energy native defects and Eu 2 + -related defect complexes. Other RE dopants, dysprosium (Dy) and erbium (Er), are stable only as Dy 3 + and Er 3 + , respectively. These results provide an explanation why it is difficult to realize Eu 3 + in bulk ZnS. A non-negligible Eu 3 + /Eu 2 + ratio might be achieved with Li co-doping under S-rich (and probably non-equilibrium) synthesis conditions. Optically, Eu-related defects can act as carrier traps for band-to-defect transitions and emit light in the visible range. To assist with experimental optical characterization of the RE defects, we include band-to-defect luminescence involving native defects (Zn vacancies) and/or non-RE impurities (Cu, Cl, and Al) that may also be present in Eu-doped ZnS samples and assign luminescence centers often observed in experiments to specific defect configurations. [ABSTRACT FROM AUTHOR]

Eu-doped GaN (GaN:Eu) is a promising solid-state material for quantum information devices owing to its ideal quantum levels. However, a decrease of Eu concentration and the unification of optical sites are required for these devices to access an Eu ion. In this article, the effect of Eu concentration on the optical properties of Mg-codoped GaN:Eu was evaluated. The photoluminescence intensity from Eu ions increased linearly with increasing Eu concentration up to 1 × 1019 cm−3, beyond which the intensity saturated. This resulted from the increase of the sharp luminescence line at 620.5 nm (site A), which has a large excitation cross section, with increasing Eu concentration in the range of low Eu concentrations; an excess Eu concentration leads to the formation of other types of optical sites with a low transfer efficiency or inactive sites. For a low Eu concentration of 3 × 1018 cm−3, all optical sites except a specific optical site corresponding to site A disappeared, and the unification of optical sites was suggested. This result is expected to be valuable to realize quantum information devices. [ABSTRACT FROM AUTHOR]

Counterfeiting has turned out to be a major area of concern these days and is becoming a serious problem worldwide. Modern technological advances have made counterfeiting of sophisticated products easy. Therefore, it is essential to search new luminescent materials to combat counterfeiting. Herein, we report that a highly luminescent YBO3:Eu3+ phosphor was synthesized by the sol-gel technique, which can be scaled up to 1 kg in a single batch at the laboratory level. This highly luminescent boron based YBO3:Eu3+ phosphor is optically active and is structurally and chemically stable. It has a particle size of ∼110 ± 10 nm, which provides a strong orange-red emission at 591 nm upon 245 nm excitation wavelength and is also excitable in the range of 280-480 nm excitation wavelengths. The structural/microstructural and photoluminescence (PL) behaviors were characterized by scanning electron microscopy, transmission electron microscopy/high-resolution transmission electron microscopy, and fluorescent spectroscopy. Furthermore, this phosphor was used to design luminescent security ink with a commercially available polyvinyl chloride gold medium for printing of security codes as investigated by photoluminescence (PL) mapping instruments. Thus, this facile method to synthesize a low-cost YBO3:Eu3+ phosphor based security ink offers a non-replicable security code for printing that can be easy to detect but is difficult to counterfeit. [ABSTRACT FROM AUTHOR]

Theoretically probing the physics underlying the photoluminescence of phosphors and predicting their thermal quenching properties are significant issues in the field of phosphor research. The electronic ground states of a series of Eu(II)-doped alkali-earth sulfide phosphors, i.e., MS:Eu2+ (M = Mg, Ca, Sr, Ba), have been analyzed using density functional theory calculations to characterize and analyze their photoluminescence properties in terms of quantum efficiency and its thermal decay tendency. Anderson's impurity model to MS:Eu2+ enables devising a physical picture of how the electronic ground states | ψ Eu − 5 d ⟩ representing the Eu(II)-5d orbitals are mixed with those of the conduction bands (CBs) of host materials. The focus is on quantitatively deducing the electron delocalization nature of | ψ Eu − 5 d ⟩ over |CB〉, especially ∑ k | ψ k M − d k ⟩ , which represents the bands formed by the d orbitals of M atoms. The ratio of the probability amplitudes of | ψ Eu − 5 d ⟩ and ∑ k | ψ k M − d k ⟩ , i.e., C Eu − 5 d / C M − d , proves to be correlated with the electron localization nature of | ψ Eu − 5 d ⟩ , thereby suggesting that this ratio can be an effective parameter for evaluating the thermal quenching tendency of photoluminescence without more precise information on the electronic excited states. Energetically small gaps and large spatial overlaps between | ψ Eu − 5 d ⟩ and |CB〉 delocalize electrons in a hybridized state, which gives these electrons the tendency to dissipate without luminescence. The results explain the rankings of the quantum yield and its temperature dependence in the MS:Eu2+ (M = Ca, Sr, Ba) systems, which follow the Dorenbos thermal quenching model, while MgS:Eu2+ does not have the same mechanistic origin. [ABSTRACT FROM AUTHOR]

We investigated the photoluminescence of Eu-doped ZnO and ZnGaxO1 + 1.5x (x = 1.8–2.8) films upon bandgap excitation to identify the occupation sites of Eu3+ ions through varying the host crystal material, substrate material, and reactant gas. Eu3+ emissions from ZnGaxO1 + 1.5x:Eu films deposited on Si and SiO2 substrates had similar spectral shapes, but their intensities were different, correlated with different defect emission levels. When depositions were carried out in H2O gas, the Eu3+ emissions from the c-axis oriented ZnO:Eu films consisted of a very sharp main peak (P1) at 612 nm and a sub-peak (P2) at 619 nm for 5D0 → 7F2 transition, whereas those from randomly oriented polycrystalline ZnGaxO1 + 1.5x:Eu films were broader and could be divided into four components (P1, P2, P3, and P4), of which the wavelengths of P1 and P2 matched those of the ZnO:Eu films. The availability of both Ga3+ and Zn2+ sites in the ZnGa2O4 lattice expands the variance of chemically distinct sites that can be occupied with Eu3+ compared with only divalent Zn2+ sites in the ZnO crystal. Films deposited with O2 exhibited lower emission intensities with a narrower spectrum width than those deposited with H2O. This behavior was correlated with the X-ray diffraction peak width of ZnGa2O4(311). High-quality crystal lattices formed with O2 allowed only a few sites to accommodate Eu3+ ions. In contrast, OH− and H+ derived from H2O will modify crystallinity to generate various emission-active sites, resulting in intense and broad emissions. Possible sites for the four components are discussed. [ABSTRACT FROM AUTHOR]

A synchrotron source offers the advantage of continuous and tunable x rays. Therefore, not only an X-ray nanoprobe can provide the desired spatial resolution to measure the elemental distribution of CaAlSiN3:Eu2+ via X-ray fluorescence mapping but X-ray absorption spectroscopy can also be used to unambiguously analyze the valence states of europium ions (Eu2+ or Eu3+) in different local areas. X-ray excited optical luminescence spectra exhibit only one red emission peak (∼650 nm) corresponding to the 4f65d1 to 4f7 transition of Eu2+, which reveals the fact that Eu2+ ions substitute perfectly for Ca2+ ions at the same site. Through detailed analysis, we demonstrated that the main contribution to the luminescence intensity of CASIN:Eu2+ comes from the Eu2+ activator in the product. We anticipate that X-ray nanoprobes will open new avenues with great characterization ability for studying the emission properties of CASIN:Eu2+. [ABSTRACT FROM AUTHOR]

Ab initio calculations on Eu doped (GaN)n (n=12, 13, and 32) nanoparticles show that Eu doping in nanoparticles is favorable compared with bulk GaN as a large fraction of atoms lie on the surface where strain can be released compared with bulk where often Eu doping is associated with a N vacancy. Co-doping of Si further facilitates Eu doping as strain from an oversized Eu atom and an undersized Si atom is compensated. These results along with low symmetry sites in nanoparticles make them attractive for developing strongly luminescent nanomaterials. The atomic and electronic structures are discussed using generalized gradient approximation (GGA) for the exchange-correlation energy as well as GGA + U formalism. In all cases of Eu (Eu+Si) doping, the magnetic moments are localized on the Eu site with a large value of 6μB (7μB). Our results suggest that co-doping can be a very useful way to achieve rare-earth doping in different hosts for optoelectronic materials. [ABSTRACT FROM AUTHOR]

Emission sites in GaN:Eu red light-emitting diodes (LEDs) were investigated using a new spectroscopy technique, namely, site-selective pulse-driven emission spectroscopy (PDES). The PDES, in which the emission intensity of a pulse-driven LED is recorded with respect to the pulse frequency, revealed the charge-trapping dynamics of the Eu emission sites. We found that a determinant of the emission intensity of the sites was not their relative abundance, but rather the spatial extent of the local potential, which determines the effectiveness of the capture of injection charges. Minor sites with wider potentials enhanced the emission intensity of the LED, resulting in emission spectra that differ from those obtained using the photoluminescence of a GaN:Eu thin film. The potential curve is determined by the atomic structure of the complexes, which consist of a Eu dopant and nearby defects in the GaN host. The extent was characterized by a parameter, namely, cutoff frequency, and the emission sites with the wider and narrower potentials in the GaN:Eu LED were found to have cutoff frequencies of 400 kHz and 3 MHz, respectively. The cutoff frequency of 3 MHz was found to be the upper limit for emission sites in the LED. The emission site with the wider potential is useful for slower devices such as light fixtures, while the site with the narrower potential is useful for faster devices such as opto-isolators. [ABSTRACT FROM AUTHOR]

The excellent optical properties of europium-doped crystals in visible and near infrared wavelength regions enable them to have broad applications in optoelectronics, laser crystals and sensing devices. The local site crystal fields can affect the intensities and peak positions of the photo-emission lines strongly, but they are usually difficult to be clarified due to magnetically degenerate 4f electronic levels coupling with the crystal fields. Here, we provide an effective way to explore the hidden local symmetry of the Eu3+ sites in different hosts by taking photoluminescence measurements under pulsed high magnetic fields up to 46 T. The zero-field photoluminescence peaks split further at high magnetic fields when the Zeeman splitting energy is comparable to or larger than that of the crystal field induced zero-field splitting. In particular, a magnetic field induced crossover of the local crystal fields has been observed in the GdVO4:Eu3+ crystal, which resulted from the alignment of Gd3+ magnetic moment in high magnetic fields; and a hexagonally symmetric local crystal fields was observed in the YPO4 nanocrystals at the Eu3+ sites characterized by the special axial and rhombic crystal field terms. These distinct Zeeman splitting behaviors uncover the crystal fields-related local symmetry of luminescent Eu3+ centers in different hosts or magnetic environments, which are significant for their applications in optics and optoelectronics. [ABSTRACT FROM AUTHOR]

Irradiation of atomic europium isolated in the solid rare gases, with low intensity laser excitation of the y8P ← α8S resonance transition at ca. 465 nm, is found to produce singly charged europium cations (Eu+) in large amounts in xenon and in smaller amounts in argon. Confirmation of the formation of matrix-isolated Eu+ is obtained from characteristic absorption bands in the U V and in the visible spectral regions. The luminescence produced with excitation of the cation bands is presented in greatest detail for Eu/Xe and assigned. Excitation of the 4f7(8S7/2)6p3/2 absorption bands of Eu+ between 390 and 410 nm produces emission which is quite distinct from that resulting from excitation of the 4f7(8S7/2)6p1/2 absorption (430 to 450 nm) features. The latter consists of narrow, resolved emission bands with Stokes shifts ten times smaller than the former. The observed spectral differences are discussed in relation to the different spatial symmetries of the p3/2 and p1/2 orbitals in these j-j coupled (7/2, 3/2)J and the (7/2, 1/2)J levels. Møller-Plesset calculations are conducted to obtain the molecular parameters of the neutral Eu-RG and cationic Eu+-RG diatomics (RG = Ar, Kr, Xe). From the short bond lengths and the strong binding energies obtained for the Eu+-RG species, these values suggest the isolation of the ion in small, possibly interstitial sites especially in xenon. In contrast, but consistent with previous work [O. Byrne and J. G. McCaffrey, J. Chem. Phys. 134, 124501 (2011)], the interaction potentials calculated herein for the Eu-RG diatomics suggest that the neutral Eu atom occupies tetra-vacancy (tv) and hexa-vacancy (hv) sites in the solid rare gas hosts. Possible reasons for the facile production of Eu+ in the solid rare gases are discussed. The mechanism proposed is that atomic europium is also acting as an electron acceptor, providing a temporary trap for the ionised electron in the matrices. [ABSTRACT FROM AUTHOR]

We observe an enhanced magnetic entropy change (-ΔSM) at cryogenic temperatures (T<20 K) in Eu8Ga16Ge30 clathrate (type-I) nanocrystals prepared by a ball milling method. With reduction in the crystal size to 15 nm, -ΔSM is enhanced at low temperatures, reaching the highest value (~10 J/kg K) at 5K for a field change of 5 T. For all samples investigated, there is a cross-over temperature (~25 K) in -ΔSM (T) above which -ΔSM decreases with crystal size, opposite to that observed at low temperatures. A careful analysis of the magnetic and magnetocaloric data reveals that as the crystal size decreases the magnetic interaction between Eu2+ ions on the Eu2 site governing the primary ferromagnetic transition at ~35K becomes gradually weaker, in effect, altering the interaction between Eu2+ ions occupying the Eu1 and Eu2 sites responsible for the secondary ferromagnetic transition at 15 K. As a result, we have observed a strong change in magnetization and the enhancement of -ΔSM at low temperature. [ABSTRACT FROM AUTHOR]

In the present work, the dynamics of the spins and the structural parameters of thermal treated samples of Eu1−xFexCrO3 (x = 0, 0.1 and 0.2) were investigated. The ac-magnetic susceptibility (χac) was measured near TN for frequencies (f) in the range 10 - 104 Hz, magnitude of the ac magnetic field of 10 Oe and for 5 ≤ T ≤ 300 K. X-ray diffraction data were used for determining the lattice parameters and the bonding angle θB (Cr– O(2) – Cr) for 100 ≤ T ≤ 300 K. The maximum in χac was found to shift to higher values of T for increasing values of f. The Vogel-Fulcher law was used for analyzing χac yielding values for the characteristic relaxation time τ0, activation energy Ea/kB and glassy temperature TG, respectively, in the ranges 2.10 - 3.96 ps, 46.5 - 47.2 K and 169.9 -176.1 K. The super-exchange parameter J ∼ cos 4 180 − θ B / 2 / d 7 , where d is the length of the bound Cr-O(2), was also obtained yielding a good correlation with the corresponding values of TN. [ABSTRACT FROM AUTHOR]

Structural and optical studies are reported of yttrium orthoborate YBO3 when tri-doped with Eu3+, Ce3+, and Tb3+, focusing on the role of terbium concentration. Incorporation of Tb3+ affects emission properties for photoluminescence (PL) excited by near ultraviolet light. For constant cerium and europium concentrations, increasing the Tb3+ results in diminished PL from the Ce3+ and Tb3+ color centers. Simultaneously, the PL excitation bands related to both Ce3+ and Tb3+ increase in intensity for red emission from the Eu3+. Results are consistent with a Ce3+→(Tb3+)n→Eu3+ energy transfer scheme, where (Tb3+)n denotes a chain incorporating n terbium ions. A high red to orange PL intensity ratio is obtained, ranging from 1.34 to 2.09. Raman vibrational bands show a systematic change, with Tb3+ concentration, in the B3O9 ring terminal oxygen bending mode coordinated with the yttrium site where dopant ions substitute. The structural changes are interpreted as variations in the local neighborhood of these sites in the YBO3:Ce3+,Tb3+,Eu3+ crystal structure. [ABSTRACT FROM AUTHOR]

Structural and optical studies are reported of yttrium orthoborate YBO3 when tri-doped with Eu3+, Ce3+, and Tb3+, focusing on the role of terbium concentration. Incorporation of Tb3+ affects emission properties for photoluminescence (PL) excited by near ultraviolet light. For constant cerium and europium concentrations, increasing the Tb3+ results in diminished PL from the Ce3+ and Tb3+ color centers. Simultaneously, the PL excitation bands related to both Ce3+ and Tb3+ increase in intensity for red emission from the Eu3+. Results are consistent with a Ce3+→(Tb3+)n→Eu3+ energy transfer scheme, where (Tb3+)n denotes a chain incorporating n terbium ions. A high red to orange PL intensity ratio is obtained, ranging from 1.34 to 2.09. Raman vibrational bands show a systematic change, with Tb3+ concentration, in the B3O9 ring terminal oxygen bending mode coordinated with the yttrium site where dopant ions substitute. The structural changes are interpreted as variations in the local neighborhood of these sites in the YBO3:Ce3+,Tb3+,Eu3+ crystal structure. [ABSTRACT FROM AUTHOR]

The luminescence from europium doped lanthanum trifluoride (Eu3+:LaF3) nano-crystals can be greatly enhanced by capping with β-diketonate organic ligands. Here, we report on photo-stability measurements for the case of nano-crystals capped with thenoyltrifluroacetone (TTA) and compared with those capped with an inactive ligand, oleic acid. With exposure to UV pump light, we observed significant decrease in fluorescence and change in emission spectrum of the TTA-capped nano-particles whilst the fluorescence lifetime remained approximately constant. After a dose of order 70 kJ cm-2, the luminescence level was similar to that of oleic acid capped nano-crystals. We discuss possible mechanisms. [ABSTRACT FROM AUTHOR]

In the present article, we analyse the possibility of sensitizing the 3Pj levels of Pr3+ ion with Eu2+ ion in CaF2 thin film deposited by evaporation. Indeed, the forbidden nature of the 4f-4f transition of Pr3+ ion makes its absorption too weak for thin film applications, while materials doped with the Pr3+-Yb3+ couple are promising candidates for the achievement of efficient down-converter systems and could allow strong reduction of thermalization losses in silicon solar cells. [ABSTRACT FROM AUTHOR]

Changes in the excitation spectra of luminescent species inserted in photorefractive crystals as a function of changes in the high-order photonic band gap (PBG) have not been previously observed. In this communication, we present our results monitoring the excitation band of Eu(TTA)3(TPPO)2 inserted in the PMMA opal photonic crystals as a function of the changes in the high-order PBG of the crystals. We find shifts in the complex excitation band and changes in the integrated emission intensity that correlates with shifts in the high-order PBG through coupling to the excitation transition. [ABSTRACT FROM AUTHOR]

The comparison of the performances of SiO2 and SiOC layers as host matrices for optically active Eu ions is presented. A SiO2 matrix allows to observe light emission from both Eu2+ and Eu3+ ions, owing to a proper tuning of the thermal annealing process used for the optical activation of the rare earth. However, the photoluminescence efficiency of both ions remains relatively low and quite far from the requirements for technological applications, mainly due to the extensive formation of Eu-containing precipitates. A detailed study by transmission electron microscopy allowed us to analyze and elucidate the clustering process and to find suitable strategies for minimizing it. We found that the substitution of SiO2 matrix with a SiOC film allows to obtain a very bright light emission centered at about 440 nm from Eu2+ ions. In fact, SiOC is able to efficiently promote the Eu3+ → Eu2+ reduction; furthermore, Eu ions are characterized by an enhanced mobility and solubility in this matrix, and as a consequence, Eu precipitation is strongly reduced. Since SiOC is a material fully compatible with standard Si technology, Eu-doped SiOC layers can be considered a highly interesting candidate for photonic applications. [ABSTRACT FROM AUTHOR]

Hydrothermally grown SnO2 and SnO2:Eu nanoparticles of 4-11 nm size range were analyzed by photoluminescence (PL) and therrmoluminescence (TL) spectroscopy to study the effect of Eu-doping on their emission behaviors. It has been observed that most of the incorporated Eu3+ ions remain at the interstitial sites of SnO2 lattice. High Eu-contents in the nanoparticles generate lattice deformation, formation of Eu3+/Eu0 clusters at interstitial sites, or segregation to their surfaces. Formation of Eu clusters at interstitial sites enhances electronic defect density in the crystal lattice, reorganizes carrier trapping centers, and modifies their activation energies. Room temperature PL emission and beta-irradiated TL dose response of SnO2 nanoparticles enhance significantly when doped with 0.5 and 1.0 mol. % nominal of Eu3+, respectively, opening up their possibilities of applications in bio-imaging and radiation therapy. Possible mechanisms of enhanced PL and TL responses of the samples have been discussed. [ABSTRACT FROM AUTHOR]

The effect of europium (Eu)-doping on the optoelectronic carrier transition properties of pseudo-cubic barium titanate (BT) nanostructured system is being reported. Referring to x-ray diffractograms, apart from the diffraction peaks related to perovskite BT structure, non-existence of any additional peaks due to byproducts has revealed that Eu has undergone substitutional doping into BT host lattice. We speculate that adequate growth of a cubic overlayer over the tetragonal core has led to suppressed tetragonality (c/a ratio) features. We notice substantial decrease in the carrier transition exponent (n value), from its normal value, when doping level was varied within 0%-14%. While the overall photoluminescence response is improved with Eu-doping, the BT system was expected to experience concentration quenching. The emission peak at ∼455 nm was attributed to Eu2+ mediated 4f65d1→4f7 carrier transitions. Investigating optoelectronic properties of non-ferroelectric perovskite nanostructured system has a direct relevance in nanoscale optics and optoelectronic components. [ABSTRACT FROM AUTHOR]

We report on the evaluation of rare earth (Er3+, Eu3+, and Tb3+ ions) SiO2 sub-micrometric spheres as potential optically controllable temperature sensors. Details about fabrication, optical manipulation and spectroscopic characterization of the sub-micrometric spheres are presented. The fluorescence properties of the micros-spheres in the biological range (25-60 °C) have been systematically investigated. From this systematic study, the thermal resolution potentially achieved in each case has been determined and compared to previous works. [ABSTRACT FROM AUTHOR]

The dual nature of the magnesium acceptor in gallium nitride results in dynamic defect complexes. Europium spectator ions reveal switching between two spectrally unique metastable centers, each corresponding to a particular acceptor state. By ion co-implantation of europium and oxygen into GaN(Mg), we produce, in addition, an anchored state system. In doing so, we create an abundance of previously unidentified stable centers, which we denote as "Eu0(Ox)." We introduce a microscopic model for these centers with oxygen substituting for nitrogen in the bridging site. [ABSTRACT FROM AUTHOR]

Our 151Eu Mössbauer investigation of Eu2In and Eu2Sn shows that the europium in both materials is fully divalent. We confirm the distinct thermodynamic orders of the magnetic transitions and reveal a remarkable difference between the magnetic environments of the europium atoms in the two compounds. Possible structural and electronic origins for these differences are discussed using DFT calculations. [ABSTRACT FROM AUTHOR]

151Eu Mössbauer spectroscopy confirms that the europium in EuAg4As2 is fully divalent and that the spectrum at 5 K consists of a single, sharp magnetic pattern with a hyperfine field (Bhf) of 27.1(1) T and an isomer shift of −11.04(3) mm/s (relative to EuF3). The temperature dependence of the spectra shows that the ordering of the Eu moments proceeds via an incommensurate sine modulated structure starting at 15 K. The structure squares up below 9 K. A search for charge density or phonon softening signatures at the 120 K structural transition was not successful. [ABSTRACT FROM AUTHOR]

We investigated the persistent luminescence in europium-doped barium chloroapatite upon codoping with cerium. Luminescence properties of the phosphors, including photoluminescence, luminescence decay, and thermoluminescence are systematically studied. This material holds the key to the unsettled questions in the field of persistent luminescence. We formulated a model of persistent luminescence on the basis of the experimental results. In our model, some Eu2+ ions are oxidized to Eu3+ under short UV excitation, and the released electrons are trapped at positive substitutional defect introduced by Ce3+. The persistent luminescence arises from the recombination of these trapped electrons with the photo-ionized Eu3+ ions. The effects of Coulomb attraction between the substitutional defect and trapped electron, along with electron-electron repulsion, construct a metastable exciton-like trap. To a first approximation, the third ionization energy and ionic radius of lanthanide codopant can be used to rationalize their influence on persistent luminescence of Eu2+. Our model can also explain other systems, such as SrAl2O4:Eu2+,R3+ (R = rare earth elements). [ABSTRACT FROM AUTHOR]

Eu doped aluminum nitride phosphors were successfully synthesized by a novel gas-reduction-nitridation route with a reaction temperature of 1400 °C and a soaking time of 3 h. The obtained AlN:Eu phosphors were analyzed to elucidate the location of the Eu luminescent center. High-resolution transmission electron microscopy and transmission electron microscopy-energy dispersive spectra proved that Eu was located in the crystal lattice of AlN, then EXAFS revealed that Eu occupied a highly distorted Al site coordinated by four nitrogen at about 2.30-2.40 Å, and the second nearest neighbors of Eu were 12 Al. This could be confirmed by the first-principles calculations based on the obtained local structure around the Eu luminescence center, where the theoretical absorption spectrum was similar to the experimental excitation spectrum. X-ray appearance near edge structure showed that Eu existed in terms of both Eu3+ and Eu2+ ions, which could be related to the limited location space of Eu. High temperature treatment could significantly increase the amount of Eu2+ by the expansion of the crystal lattice, leading to an increased green luminescence of the obtained AlN:Eu phosphors. [ABSTRACT FROM AUTHOR]

The structure/property relationships of fluorochlorozirconate glass ceramics as a function of divalent and trivalent europium (Eu) co-doping and thermal processing have been investigated; the influence of doping ratio on the formation of barium chloride (BaCl2) nanocrystals therein was elucidated. X-ray absorption near-edge structure spectroscopy shows that the post-thermal annealing changes the Eu valence of the as-poured glass slightly, but during the melting process Eu3+ is more strongly reduced to Eu2+, in particular, when doped as a chloride instead of fluoride compound. The Eu2+-to-Eu3+ doping ratio also plays a significant role in chemical equilibrium in the melt. X-ray diffraction measurements indicate that a higher Eu2+ fraction leads to a BaCl2 phase transition from hexagonal to orthorhombic structure at a lower temperature. [ABSTRACT FROM AUTHOR]