State Of Eu3 Research Articles

Luminescent color modulation of Zn/BaAl2O4:0.2%Eu phosphors for LED application

Spinel-type aluminate (ZnAl2O4) doped with europium (Eu) ions has garnered considerable attention in the field of luminescence. This study explores a series of Zn/BaAl2O4:0.2%Eu phosphors (x=0∼0.25, x is for the mole fraction of BaAl2O4), fabricated through a high temperature solid-phase reaction method in air or reduction environment. In the case of phosphors synthesized in air, the photoluminescence emission (PL) spectra show a series of sharp emission peaks at 570nm, 589nm, 620nm, 660nm, and 710nm, which are generated by the 5D0-7FJ (J = 0, 1, 2, 3, 4) level transitions in Eu3+. Time-resolved photoluminescence and X-ray photoelectron spectroscopy (XPS) characteristics also validate the presence of Eu3+ in samples synthesized in air. An intriguing observation is the abnormally strong emission peak at 570nm under 346nm excitation, originating from the Eu3+5D0-7F0 level transition. For x=0.15, the corresponding CIE color coordinate is (0.3246, 0.3449), suggesting its potential application as a mono-doped and uni-matrix white phosphor. On the other hand, phosphors synthesized in reduction environment exhibit PL spectra with a wide emission band spanning from 400nm to 550nm, resulting from the electric-dipole-allowed transition of f-d state of Eu2+. The partial substitution of Zn2+ with Ba2+ significantly enhances the Eu2+ luminescence intensity. Moreover, an elevation of the mole fraction of Zn/BaAl2O4:0.2%Eu leads to a notable redshift (450nm→500nm) in the emission peaks of Eu2+ caused by lattice expansion, providing the adjustability of emitting color.

Quaternary Selenides EuLnCuSe3: Synthesis, Structures, Properties and In Silico Studies.

In this work, we report on the synthesis, in-depth crystal structure studies as well as optical and magnetic properties of newly synthesized heterometallic quaternary selenides of the Eu+2Ln+3Cu+1Se3 composition. Crystal structures of the obtained compounds were refined by the derivative difference minimization (DDM) method from the powder X-ray diffraction data. The structures are found to belong to orthorhombic space groups Pnma (structure type Ba2MnS3 for EuLaCuSe3 and structure type Eu2CuS3 for EuLnCuSe3, where Ln = Sm, Gd, Tb, Dy, Ho and Y) and Cmcm (structure type KZrCuS3 for EuLnCuSe3, where Ln = Tm, Yb and Lu). Space groups Pnma and Cmcm were delimited based on the tolerance factor t’, and vibrational spectroscopy additionally confirmed the formation of three structural types. With a decrease in the ionic radius of Ln3+ in the reported structures, the distortion of the (LnCuSe3) layers decreases, and a gradual formation of the more symmetric structure occurs in the sequence Ba2MnS3 → Eu2CuS3 → KZrCuS3. According to magnetic studies, compounds EuLnCuSe3 (Ln = Tb, Dy, Ho and Tm) each exhibit ferrimagnetic properties with transition temperatures ranging from 4.7 to 6.3 K. A negative magnetization effect is observed for compound EuHoCuSe3 at temperatures below 4.8 K. The magnetic properties of the discussed selenides and isostructural sulfides were compared. The direct optical band gaps for EuLnCuSe3, subtracted from the corresponding diffuse reflectance spectra, were found to be 1.87–2.09 eV. Deviation between experimental and calculated band gaps is ascribed to lower d states of Eu2+ in the crystal field of EuLnCuSe3, while anomalous narrowing of the band gap of EuYbCuSe3 is explained by the low-lying charge-transfer state. Ab initio calculations of the crystal structures, elastic properties and phonon spectra of the reported compounds were performed.

Nanocrystalline Eu-doped PrB6 hexaborides with tunable optical absorption: A combined experimental and density functional theory study

Nanocrystalline Eu-doped PrB6 ultrafine powders have been successfully fabricated through solid-state chemical reaction of Eu2O3, PrCl3 and NaBH4 as raw materials. The optical absorption properties of the synthesized samples were investigated by experimental measurement and theoretical calculation. As a result, a strong red-shift of transmittance wavelength of nanocrystalline PrB6 is achieved via altering the Eu doping. Theoretically, the doping of divalent Eu into trivalent PrB6 reduces the plasma frequency excitation energy and increases the corresponding transmittance wavelength. Additionally, the synchrotron radiation absorption shows that Pr and Eu atoms exist in the form of Pr3+ in PrB6 and Eu2+ in EuB6, and X-ray photoelectron spectroscopy results also indicate that Eu exists in the state of Eu2+ in the nanocrystalline Pr0.4Eu0.6B6, which confirms that the Eu doping reduces the number of conduction electrons in PrB6 and decreases the plasma frequency excitation energy.

Synthesis and photoluminescence properties of the Eu(III)-containing silica nanoparticles via a mechanochemical solid-state reaction between SiO2 and EuCl3·6H2O

In this study, Eu3+-containing amorphous silica nanoparticles and Eu compounds were successfully synthesized via a mechanochemical solid-state reaction between silica nanoparticles and EuCl3·6H2O. This reaction was induced by a grinding process, and the states of Eu3+ in the silica/europium composites were investigated. The silica/europium composites exhibited orange–red color luminescence owing to the 5D0–7F0, 5D0–7F1, and 5D0–7F2 transitions, which indicated the presence of Eu3+ in the silica framework and the newly formed Eu compounds such as EuOCl and Eu(OH)2Cl. The mechanochemical reaction because of the grinding process effectively induced an interaction between the silica surface and europium chloride; subsequently, Eu(OH)2Cl was formed in the silica/europium composites. Additionally, the Eu(OH)2Cl in the silica/europium composite exhibited a higher thermal stability than that of simple Eu(OH)2Cl, indicating that the mechanochemical reaction mediated the formation of Eu(OH)2Cl and new chemical bonding between the newly formed Eu(OH)2Cl and the silica surface, providing improved thermal stability to Eu(OH)2Cl. Thus, we successfully prepared silica nanoparticles containing not only Eu(III) in the silica framework but also Eu compounds that exhibit unique chemical bonding during a mechanochemical reaction.

Discovery, Crystal Growth, and Characterization of Garnet Eu2PbSb2Zn3O12

Single crystal specimens of previously unknown garnet Eu2PbSb2Zn3O12 were grown in a reactive PbO:PbF2 flux medium. The crystals were characterized by a combination of X‐ray crystallography, magnetization measurements, and the optical techniques of Raman, photoluminescence, and UV/Vis spectroscopy. The material exhibits Van Vleck paramagnetism associated with the J = 0 state of Eu3+, which was possible to accurately fit to a theoretical model. Band structure calculations were performed and compared to the experimental band gap of 1.98 eV. The crystals demonstrate photoluminescence associated with the 4f 6 configuration of the Eu3+ ions sitting at the distorted 8‐coordinate garnet A site. The title compound represents a unique quinary contribution to a relatively unexplored area of rare earth bearing garnet crystal chemistry.

Charge states of the activator and size effects in BaF2: Eu nanophosphors

ABSTRACT According to the spectra of stationary X-ray excited luminescence (XEL) of BaF2: Eu nanophosphors at 80 and 294 K, it was revealed that the thermal annealing of fine-grained nanoparticles (d = 35 nm) in the range of 400–1000°C, which is accompanied by an increase of their sizes in the range of 58–120 nm, does not result in effective changes of the charge state of Eu3 + → Eu2 + activator, in contrast to CaF2: Eu nanoparticles. The maximum light output of X-ray excited luminescence of BaF2: Eu nanophosphors in the 590 nm emission band of Eu3+ ion was observed at an annealing temperature of 600°C with the average size of nanoparticles 67 nm. The subsequent growth of annealing temperatures, especially in the range of 800–1000°C, causes decrease in the light output of X-ray excited luminescence due to the increase of defect concentration in the lattice as a result of sharp increase of nanoparticle sizes and their agglomeration. In BaF2: Eu nanoparticles of 58 nm size, according to the thermostimulated luminescence (TSL) spectrum, transformation of Eu3+ → Eu2+ under the influence of long-time X-ray irradiation was revealed for the peak of 151 K. Thus, X-ray excited luminescence spectra of BaF2: Eu nanophosphors are formed predominantly due to the emission of Eu3+ ions, while emission of Eu2+ ions is observed in the TSL spectra.

Mixed-Valence Lanthanide-Activated Phosphors: Invariance of the Intervalence Charge Transfer (IVCT) Absorption Onset across the Series

Recently, direct evidence was given for the existence of intervalence charge transfer (IVCT) states of Eu2+/Eu3+ pairs in Eu-doped fluorite hosts and their signature in absorption spectra was characterized [J. Phys. Chem. Lett. 2019, 10, 1851]. Here we show, by means of multiconfigurational ab initio calculations, that the IVCT absorptions of all 2+/3+ mixed valence lanthanides doped in CaF2 start basically at the same energy. This is rationalized with a simplified model of IVCT absorptions. Emissions above that energy are expected to be partly or totally quenched when 2+/3+ pairs are formed. On the basis of this finding and existing calculations, we report expected IVCT absorptions of mixed valence lanthanides doped in several fluoride, oxide, and sulfide hosts.

Absorption intensity analysis and emission properties KEu(PO3)4 and KEuxY1-x(PO3)4 crystals

Abstract Optical absorption, excitation and emission spectra of Eu3+ ions in stoichiometric KEu(PO3)4 and KEuxY1-x(PO3)4 crystals were investigated. Strong, red emissions of Eu3+ centered at 617 and 700 nm originates mainly from the 5D0 →7F2+7F4 transitions respectively. Judd-Ofelt intensity parameters for f-f transitions were derived from the emission spectra and also from the integrated absorption spectra. These parameters were used to calculate the radiative transition rates (AR), lifetimes (τR) and branching ratios β for 5D0 excited state of Eu3+. The calculated values of τR and β were compared with the measured values for 5D0 level. The 5D0 fluorescence decay time in pure KEu(PO3)4 was exponential and quite long, of 3.93 ms. The stimulated emission cross-sections σ were also evaluated for the 5D0 → 7FJ transitions for the first time in this system.

Direct Evidence of Intervalence Charge-Transfer States of Eu-Doped Luminescent Materials

Direct evidence is given for the existence of intervalence charge transfer (IVCT) states of Eu2+/Eu3+ pairs in Eu-doped CaF2, SrF2, and BaF2. They are detected in diffuse reflectance spectra. In doped materials, IVCT states, in which an electron transfer occurs between two metal sites differing only in oxidation state, are rather difficult to observe because the absorption bands are extremely broad and flat, their intensity is low, and no emission follows the IVCT absorptions. Their assignment as IVCT states is provided by state-of-the-art multiconfigurational ab initio calculations. Although IVCT states of lanthanide-doped materials have largely been overlooked so far, they can cause luminescence quenching and even complete luminescence excitation loss. Their direct observation and independent assignment in classical dopant (Eu) and hosts (CaF2, SrF2, BaF2) are very significant: They suggest that the occurrence of IVCT states in other lanthanide-activated materials is very likely overlooked and their impact is ignored.

Spectral attributes of Eu3+ doped borotellurite glasses containing Mn3O4 nanoparticles

Glass samples of composition (59-x)TeO2-30B2O3-10MgO-1Eu2O3-xMn3O4, where x = 0, 0.5, 1.0, 1.5 and 2.0 mol % were prepared using melt quenching method. The Mn3O4 nanoparticles (MNPs) concentration dependent spectral properties were determined. XRD pattern verified the amorphous nature of prepared glasses and the presence of MNPs inside the glass matrix. TEM images revealed the nucleation of MNPs of average diameter 15 ± 1 nm. High resolution TEM data confirmed the NPs growth along (1 0 3) crystal plane orientation having lattice spacing ≈ 0.276 nm. Raman spectra displayed a shift in the vibrational modes of TeO4 and TeO3 units and thereby confirmed the alteration in the glass network structures mediated by NPs. The bonding characteristics of Eu3+ and ligand field parameters were evaluated. The observed increase in the network covalency was attributed to the MNPs assisted changes in the electron distribution. The emission spectra of glass samples revealed five prominent peaks centred at 578 nm, 591 nm, 610 nm, 651 nm and 700 nm which were assigned to the transition from 5D0→7FJ (J = 0, 1, 2, 3, 4) states of Eu3+ ion. Judd-Ofelt intensity parameters were calculated. The prepared glasses exhibited paramagnetic behaviour. EPR spectra verified the predominant occurrence of Mn2+ with effective g ≈ 2.0.

Modified magnetic and optical properties of manganese nanoparticles incorporated europium doped magnesium borotellurite glass

This paper reports the modified optical and magnetic properties of europium (Eu3+) ions doped and Manganese nanoparticles (NPs) embedded Magnesium Borotellurite glass synthesized via melt quenching method. The influence of varying Mn NPs concentrations on the magnetic, absorption and emission properties of such glass samples are determined. Stables, transparent and amorphous glasses are obtained. The observed modification of the electronic polarizability is interpreted in terms of the generation of non-bridging oxygen (NBO) and bridging oxygen (BO) in the amorphous network. TEM images manifested the growth of Mn NPs with average diameter 11±1nm. High-resolution TEM reveals that the lattice spacing of manganese nanoparticles is 0.308nm at (112) plane. The emission spectra revealed four prominent peaks centered at 587nm, 610nm, 651nm and 700nm assigned to the transition from 5D0 →7FJ (J=1, 2, 3, 4) states of Eu3+ ion. A significant drop in the luminescence intensity due to the incorporation of Mn NPs is ascribed to the enhanced energy transfer from the Eu3+ ion to NPs. Prepared glass systems exhibited paramagnetic behavior.

Crystal Structure, Spectroscopic Studies and Thermal Behavior of a New Type Lanthanide Diphosphate HYbP2O7·5H2O

A new ytterbium diphosphate HYbP2O7·5H2O has been synthesized and characterized by single crystal X-ray diffraction. The compound belongs to the monoclinic P21/c space group, and its unit cell dimensions are: a = 6.845(1), b = 8.739(2), c = 17.342(4) A, β = 90.61(2)°, V = 1037.3(4) A3, Z = 4. The framework of this compound consists of layers, parallel to the ab plane, formed by HP2O7 groups and YbO7 polyhedra. They are interconnected by strong hydrogen bonds involving the acidic hydrogen and external oxygen atoms of adjacent diphosphate groups. This layer organization generates channels parallel to the a axis in which two crystallization water molecules are located. The remaining three water molecules complete the coordination sphere of the ytterbium cation. TG and DTA thermograms of the title compound show four decomposition steps, in the 298–1173 K temperature range, corresponding to the removal of the five crystallization water molecules and the acidic hydrogen. A mixture of monophosphate YbPO4 and ytterbium polyphosphate YbP3O9 is obtained at 1173 K. IR and Raman spectra of HYbP2O7·5H2O have also been investigated. Most of the IR bands are non-coincident with those observed in the Raman spectrum, as expected for a centrosymmetric crystal. The emission spectrum of 10 % Eu3+-doped HYbP2O7·5H2O was measured at room temperature and the Stark energy states of Eu3+ were calculated. The non-degenerate 5D0 → 7F0 transition confirms the unicity of the crystallographic site occupied by the lanthanide cation.

Structure, Ferroelectric and Photoluminescence Properties of Eu-Doped CaBi4Ti4O15 Multifunctional Ceramics

Lead-free multifunctional ceramics of CaBi4−xEuxTi4O15 were prepared by a traditional solid state method, and the effects of Eu doping on structure, ferroelectric, piezoelectric and photoluminescence properties of the ceramics were investigated. All the ceramics possessed typical bismuth layer structure with m = 4, belonging to orthorhombic symmetry, and no secondary phase was detected. The plate-like grains were observed in all the ceramics, and the grain growth was slightly inhibited after the addition of Eu. Saturated polarization hysteresis loops were observed for all the ceramics, and the remanent polarization Pr decreased with Eu doping. The Eu-doped ceramics had a sharp excitation band centered at 465 nm due to the f–f transition from the 7F0 ground state to the 5D2 excited state of Eu3+. Under the excitation by 465 nm light, the main emission peaks located at 595 nm and 616 nm were obtained, which corresponds to the transition of 5D0–7F1, 5D0–7F2 levels in Eu3+, respectively. Our study shows that CaBi4Ti4O15 ceramics may be a promising multifunctional material for potential applications in optical-electro integration devices.

Luminescence enhancement in Eu3+, Sm3+ co-doped liy(MoO4)2 nano-phosphors by sol-gel process.

A series of LiY(0.95-x)Eu(0.05)Sm(x)(MoO4)2 red light emitting phosphors were synthesized by sol-gel technique. The phase impurity and spectroscopic properties were characterized by X-ray Diffraction (XRD), Photo-Luminescence (PL) and Photo-Luminescence Excitation (PLE) spectra, respectively. It is found that the PLE spectra of the Eu3+, Sm3+ co-doped nanoparticles are enhanced and broadened as compared with the solely doped samples, which will make the co-doped phosphors match better with blue and/or UV GaN based LED chips. The red emission intensity of Eu3+ is largely enhanced by the energy transfer from Sm3+. The mechanism of the enhancement is clearly proven to be the increase in the quantum efficiency of 5D0 state of Eu3+ rather than the increase in the absorption of Eu3+. Meanwhile, the characteristic f-f transitions of Sm3+ are greatly reduced, resulting in little influence in the color purity of the co-doped phosphors. The present material is an amendatory promising red light emitting phosphor for white LEDs.

Synthesis and optical properties of Eu3+ doped ZnO nanoparticles used for white light emitting diodes.

ZnO nanoparticles doped with trivalent europium ions (Eu3+) were synthesized by the hydrothermal method. The structural properties of the samples were investigated by the X-ray diffraction (XRD). The results indicated that Eu3+ was incorporated into the lattice of ZnO. Photoluminescence (PL) measurements of ZnO:Eu3+ showed a strong red luminescence emission. Specially, the red emission can be obtained even under the nonresonant excitation of 320 nm, and it is explained by an energy transfer mechanism in which the energy is transferred from ZnO matrix to Eu3+. These results indicate that the ZnO:Eu3+ is the attractive candidate phosphor for the application in phosphor-converted light-emitting diodes (pc-LEDs) as red phosphor. The intensity of Eu3+ PL decreased with the increasing Eu3+ concentration and the concentration quenching mechanism was presented based on non-radiative recombination processes in ZnO and the energy back-transfer from the excited state of Eu3+ to the ZnO host. Moreover, the samples were synthesized under low temperature condition.

Preparation of Electrospun Pyrochlore-Structure KGdTa<SUB>2</SUB>O<SUB>7</SUB>:Eu<SUP>3+</SUP> Phosphor: The Optical and Structural Properties for White Light Emitting Diode Applications

Red emitting nanofibers, KGdTa2O7:Eu3+ were synthesized by electrospinning technique followed by heat treatment. As-prepared uniform fiber precursor with diameter ranging from about 700 nm to about 900 nm were calcined after removing organic species by calcination. The fiber surface become rough and diameter decreased to about 250-340 nm range due to decomposition of organic species and formation of inorganic phase. Morphology, structural and photoluminescent properties of fibers were analyzed using thermogravimetric and differential thermal analysis (TG-DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and photoluminescence (PL). TG-DTA analysis indicates that KGdTa2O7:Eu3+ began to crystalize at 520 degrees C. Fibers annealed at 900 degrees C formed well crystallized uniform fibers. Under ultraviolet excitation KGdTa2O7:Eu3+ exhibits red emission due to transitions in 4f states of Eu3+. The excitation band is dominated by the Eu(3+)--O2-charge transfer band peaked at 289 nm. The emission peak is in the region that is ideal for red light emission.

Oscillator strengths of absorption transitions from the 5 D 0 state in huntite-like EuAl3(BO3)4 polycrystals

Oscillator strengths of absorption transitions from the metastable 5 D 0 state of Eu3+ ions in aluminoborate polycrystals with the huntite structure were determined using crystal-field theory. It was established that the oscillator strength of the 5 D 0 → 5 F 4 transition, which was resonant with the 5 D 0 → 7 F 2 transition, was many times greater than that for other resonant transitions of Eu3+ ions. The transition 5 D 0 → 5 H 6 had the minimum oscillator strength among such resonant absorption transitions.

Synthesis and characterization of structural and luminescence properties of blue — green BaAlxOy:Eu2+ phosphor by solution — combustion method

Abstract Europium-doped barium aluminate (BaAlxOy:Eu2+) phosphors were obtained at low temperatures (500°C) using the solution — combustion of corresponding metal nitrate-urea solution mixtures. The particle size and morphology and the structural and luminescent properties of the synthesized phosphors were examined by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), Electron diffraction spectroscopy (EDS) and photoluminescence (PL). It was found that the change in Ba: Al molar ratios showed greatly influence not only on the particle size and morphology, but also on their PL spectra and crystalline structure. The structure of BaAlxOy nanophosphors changes from a hexagonal Ba2Al10O17 phase for samples with 6:100 molar ratios to a hexagonal BaAl2O4 one with an increase in Ba content. The peak of the emission band occurs at a longer wavelength (around 615 nm) with a decrease in Ba concentration but displays a broad blue-green emission band composed from two emissions with the maximum at 495 and 530nm coming from Eu2+ in two sites for increasing Ba content. The blue-green emission is probably due to the influence of 5d electron states of Eu2+ in the crystal field because of atomic size variation causing crystal defects while the red emission is due to f - f transitions. These findings clearly demonstrate the possibility of fine tuning the colour emission.

Structural and optical investigations of Eu3+ ions in lead containing alkali fluoroborate glasses

Lead containing alkali fluoroborate glasses (LAFB) with molar composition of 20PbO+5CaO+5ZnO+10AF+59B2O3+1Eu2O3 (where A=Li, Na and K) were prepared and investigated by the TG-DTA, FT-Raman, optical absorption, fluorescence and decay curve analysis. The influence of alkali content on the structure of borate glasses was investigated by FT-Raman spectroscopy. The thermal properties of the glasses have been studied by TG-DTA analysis. Judd–Ofelt intensity parameters are derived from the absorption spectra and also from the emission spectra under various constraints. The effect of thermalization on the oscillator strengths of the absorption transitions originating from the ground (7F0) and the first excited (7F1) states of Eu3+ ions have been discussed. The J–O intensity parameters obtained by applying thermal correction to 7F0→5D2 and 7F6 absorption oscillator strengths were used to calculate the various spectroscopic properties. The predicted values of radiative lifetime (τR) and luminescence intensity branching ratio (βR) are compared with the measured values for 5D0 level. The decay profiles were found to be single exponential in all the three glasses. The spectroscopic properties confirm the potentiality of present LAFB glasses doped with Eu3+ ions as laser host materials to produce an intense red luminescence at 612nm corresponding to 5D0→7F2 emission level and have significant importance in the development of emission rich optical systems.

Effect of ion irradiation on optoelectronic properties of Ba0.12Sr0.88SO4: Eu phosphor

Nanocrystalline Ba0.12Sr0.88SO4 phosphor doped with Eu at 0.1mol% optimum concentration was prepared by the chemical co-precipitation method. X-ray diffraction study of the prepared sample suggests the orthorhombic structure with an average grain size of 62nm. The band gap was found to be 4.3eV. The samples were irradiated with 1.2MeV argon ions at fluences varying between 1011 and 1015ions/cm2, i.e. in the dose range of 59kGy to 590MGy. A prominent photoluminescence (PL) emission peak is seen around 376nm due to transition from an excited state 4f65d to 8S7/2 state of Eu2+ ions. The broadening of bands in FTIR spectrum at 1110, 990, 643 and 617cm−1 is an evidence of the generation of SO4−, SO3−, SO2−, O−, etc. radicals after ion irradiation. The effect of ion irradiation on luminescence properties was studied.