Site Symmetry Of Eu3 Research Articles

A New Look at the Explanation of Differences in Properties between La3+ and Lu3+ Titanate Hosts Occupied by Eu3+

In order to improve the quality of WLEDs, considerable efforts have been devoted to investigate red phosphor. In this study, two double perovskites La2MgTiO6 and La2ZnTiO6 and two novel pyrochlores Lu2MgTiO6 and Lu2ZnTiO6 doped with 1%Eu3+ were synthesized by the co-precipitation method. The crystal structure, absorption, excitation, and emission spectra of all samples were investigated in detail. Dissimilar luminescent behaviors of the studied samples were observed. Due to the different site symmetry of Eu3+, each compound exhibits a different emission spectrum. The emission of the magnetic dipole transition is dominant in all the spectra of the Lu-based hosts, while the forced electric dipole transition is the strongest one in the spectra of the others. Besides, the ones crystallized in double perovskite structures possess larger bandgaps and show a more intense emission from the 5D1 level of Eu3+ as compared to the pyrochlore compounds. Furthermore, the distinct mechanism of the cross-relaxation of four titanate compounds was investigated. The above findings contribute to the understanding of the two novel pyrochlore hosts.

Crystal formation in Eu3+ - Doped oxyfluorophosphate glass-ceramics for luminescence thermometry

Eu3+ doped-Oxyfluorophosphate glasses with a general composition 75 NaPO3 - (25-x) CaO – x CaF2 (with x ranging from 0 to 25 mol%) were prepared and their spectroscopic changes induced by the addition of fluorine and when applying a thermal treatment in order to grow crystals in the glasses were investigated. The addition of CaF2 at the expense of CaO reduces Ω2 and Ω4 parameters indicating that the Eu3+ ions are located in less covalent and well separated sites in oxyfluorophosphate glasses. An increase in the CaF2 content at the expense of CaO also leads to an increase in the absolute thermometric sensitivity from (4.2 × 10−4) K−1 to (17.6 × 10−4) K−1 at 523 K while decreasing the relative thermometric sensitivity from 3.0% to 1.4%.The heat treatment leads to the precipitation of crystals, the composition of crystal phase depends on the glass composition. For the glasses with x = 0 and 10, the thermal treatment increases Ω6 while reducing Ω4, as a result of an enhanced stiffness and reduced covalency of dopant's environment due to the precipitation of various crystals. As Ω2 remains unchanged, the Eu3+ are suspected to remain mainly in the amorphous part of the glass-ceramics in agreement with the lack of sharp peaks in the emission spectrum. For the glasses with x = 20 and 25, Ω2 increases indicating a change in the site symmetry of Eu3+ resulting from the dopant entering the CaF2 crystalline phase. Due to the changes in the Eu3+ sites in the heat treated glasses, the heat treatment of the glass increases the absolute thermal sensitivity, but reduces the relative thermal sensitivity. The oxyfluorophosphate glass-ceramic with x = 25 exhibits high absolute thermometric sensitivity compared to oxyfluorophosphate glass, but also comparatively low relative sensitivity of 0.5% K−1.

Novel Sol-Gel Route to Prepare Eu3+-Doped 80SiO2-20NaGdF4 Oxyfluoride Glass-Ceramic for Photonic Device Applications.

Oxyfluoride glass-ceramics (OxGCs) with the molar composition 80SiO2-20(1.5Eu3+: NaGdF4) were prepared with sol-gel following the "pre-crystallised nanoparticles route" with promising optical results. The preparation of 1.5 mol % Eu3+-doped NaGdF4 nanoparticles, named 1.5Eu3+: NaGdF4, was optimised and characterised using XRD, FTIR and HRTEM. The structural characterisation of 80SiO2-20(1.5Eu3+: NaGdF4) OxGCs prepared from these nanoparticles' suspension was performed by XRD and FTIR revealing the presence of hexagonal and orthorhombic NaGdF4 crystalline phases. The optical properties of both nanoparticles' phases and the related OxGCs were studied by measuring the emission and excitation spectra together with the lifetimes of the 5D0 state. The emission spectra obtained by exciting the Eu3+-O2- charge transfer band showed similar features in both cases corresponding the higher emission intensity to the 5D0→7F2 transition that indicates a non-centrosymmetric site for Eu3+ ions. Moreover, time-resolved fluorescence line-narrowed emission spectra were performed at a low temperature in OxGCs to obtain information about the site symmetry of Eu3+ in this matrix. The results show that this processing method is promising for preparing transparent OxGCs coatings for photonic applications.

Glowing selenates: novel alkaline earth nanoparticles.

Up to now, no selenate nanoparticles have been described even though much research has been done on respective oxidic compounds such as sulfates and phosphates. For the first time, alkaline earth selenates of the composition MSeO4 (M = Ca, Sr, Ba) were synthesized as nanoparticles or nanorods as described in this publication. For this purpose, a micro emulsion method was applied using CTAB as a surfactant. Using X-ray diffraction measurements (XRD) phase purity of the materials could be proven. Furthermore, the nanoparticles were analyzed by raster electron microscopy (REM) and dynamic light scattering (DLS) measurements. Finally, the products were doped with small amounts of Eu3+ to obtain luminescent materials. Successful doping was demonstrated by luminescence investigations in the region of 18 000 to 14 000 cm-1 (550-715 nm). Incorporation of Eu3+ led to strong red-emitting nanoparticles. Low temperature measurements at 10 K allowed conclusions about the site symmetry of Eu3+ ions located on the alkaline earth sites.

Electrically tunable polarized luminescence from guest-host composites via interaction between rare earth complexes and liquid crystals.

Polarized luminescence has many applications in energy saving, displays, communication and other fields. Here, electrically tunable polarized luminescence of aligned Eu(tta)3phen/E7 composites is successfully obtained based on the interaction between liquid crystal (LC) hosts and rare earth (RE) complex guests. The generation mechanism of the polarization effect is thoroughly explored from three different aspects. The polarized luminescence of Eu(tta)3phen/E7 composites is closely related to the polarized energy absorption of incident light, the site symmetry of Eu3+ ions for oriented Eu(tta)3phen complex molecules, and the polarized energy transfer from E7 to Eu(tta)3phen. The convenient control of the well-aligned Eu(tta)3phen complex by simply embedding the Eu(III) complex guest in the E7 host and utilizing small-magnitude electric field forces is explicitly confirmed. The E7 host not only provides the orientation condition for the electrically tunable polarized luminescence but also promotes the degree of polarization through polarized energy transfer. The polarized spectral properties and the symmetry of the Eu3+ site of the aligned Eu(tta)3phen complexes are described in detail. The analysis of the generation mechanism of polarized luminescence supplements the research content in the field of RE/LC composites and paves the way for exciting novel advances in the field of polarized emission.

Influence of rare earth substitution on structure, photoluminescence emission properties and Judd-Ofelt analysis of ZnS:Eu3+ red phosphors

A series of Eu3+ doped ZnS red emitting phosphors were synthesized by conventional low temperature solid state reaction technique. The structural and spectroscopic characteristics of the prepared materials were examined by theoretical and experimental methods. The XRD results confirm the formation of hexagonal structured ZnS material. Similar morphology is obtained from TEM and SEM analysis and the particle size and grain size were calculated. The compositional analysis using EDS confirms the atomic percentage present in the materials. The optical band gap energy of the samples varied from 3.59 to 3.43 eV. The PL emission under excitation 390 nm has greater emission intensity at concentration x = 0.1 in Zn(1-x)S: xEu3+ material. The intense red emission (614 nm) for concentration x = 0.1 have CIE coordinates (0.6090, 0.3905) with color purity 90.41% and CCT 1629.26 K. The site symmetry of Eu3+ ions was explained using PL emission spectra. The intensity parameters Ω2, Ω4 and Ω6, radiative properties like branching ratio (βR), transition radiative parameter (AR), stimulated emission cross section σe, radiative life time (τR) was calculated from Judd-Ofelt theory. The luminescence decay kinetics was analyzed and the life time of material was calculated in millisecond (ms) range. The strong and intense red emission and the improved stimulated emission cross section offer Eu3+ doped ZnS material useful for designing optoelectronic device applications.

Structure and luminescence properties of multicolor phosphors with excellent thermal stability based on a new phosphate Ba3In4(PO4)6

A new phosphate Ba3In4(PO4)6 has been discovered in the exploration of novel host materials for color-tunable phosphors in BaO-In2O3-P2O5 system. The crystal-structure determination using powder XRD data reveals it belongs to the cubic langbeinite structure type (S.G. P213), unlike Mg3In4(PO4)6 crystallizing the triclinic system (S.G. P1¯). The existence of PO4 has been verified by IR spectra of the title compound. DTA and experimental indicate that this new phosphate has a high melting point of ∼1293 °C. Combined with calculated electronic structure and experimental UV-Vis diffuse reflectance spectrum, it has a wide direct energy band gap which is favorable for host materials. The site symmetry of Eu3+ ions and the cross relaxation of Tb3+ ions in this matrix have been clarified according to their luminescence properties. Red-pink-green tunable emission can be realized adjusting the Eu3+ and Tb3+ contents. The quantum yields of representative phosphors under the excitation of 370–392 nm ultraviolet radiation have been measured and discussed. The PL intensity of Ba3In4(PO4)6: 0.02Eu3+, 0.015 Tb3+ phosphor at 423 K of is about 67% of that at 298 K. Present results indicate that the Ba3In4(PO4)6-based phosphors are valuable for the multicolor and stable thermal performance in the display and lighting fields.

Pressure and Temperature Study on the Structural Stability of GdNbO4:Eu3+

Lanthanide niobate is an excellent nonlinear optical and high dielectric constant material. However, development and application of these novel properties depend on an understanding of its structural stability. In this work, Raman and luminescence spectra of GdNbO4 with different Eu3+ ions doping concentrations under high pressure and low temperature were obtained. The evolution of Raman spectra indicated that an irreversible structural phase transition of GdNbO4 from monoclinic phase to M′-fergusonite phase occurred at 6.2 GPa, and the phase transition was completed at about 13.1 GPa. An obvious discontinuity on Eu3+ ions luminescence intensity ratio between the 5D0 → 7F2 and the 5D0 → 7F1 transition lines was observed with increasing pressure. The results indicated that the site symmetry of Eu3+ ions in GdNbO4:Eu3+ was changed, which was in agreement with high-pressure Raman spectra data. Meanwhile, Raman and luminescence spectra showed that the crystal structure remained stable in the temperature range...

Structures, and luminescence and magnetic properties of Ln(III) complexes bearing dibenzoylmethane ligand (Ln=Eu and Gd)

The single crystal structure, luminescence and magnetic susceptibility of Cs[Ln(DBM)4] and Ln(DBM)3(phen) (Ln=Eu and Gd, DBM=dimenzoylmethanto and phen=1,10-phenanthroine) were characterized in detail. A pentanuclear Eu(III) cluster with the formula, Eu5(DBM)10(OH)5, was obtained from Cs[Eu(DBM)4] in ethanol, while from Cs[Gd(DBM)4] in acetonitrile, a one-dimensional polymeric Gd(III) assembly with the formula, {Cs[Gd(DBM)4]}n, was achieved via a heterobimetallic backbone, composed of alternating Cs and Gd atoms bridged by DBM. Exciting the Eu(III) complexes with near-UV light produced sensitized red emission by energy transfer from the triplet excited state of DBM to the Eu(III) ion. Replacing DBM by phen increased the quantum yield from Q=8.3% for Cs[Eu(DBM)4] to Q=16.6% for Eu(DBM)3(phen). This was attributed to a reduction in the site-symmetry of Eu(III) from D4h to C2v. The magnetic susceptibilities of the synthesized Ln(III) complexes in the crystalline or powder states were measured using a SQUID magnetometer. The Eu(III) complexes illustrated magnetic anisotropy at low temperatures and temperature-dependent susceptibilities. The coercive field inducing the magnetic anisotropy of Eu5(DBM)10(OH)5 was more than 40-fold stronger than those of Cs[Eu(DBM)4] and Eu(DBM)3(phen). In particular, the calculation based on the Van Vleck׳s treatment confirmed that the thermal mixing between the excited and ground states played a key role in the temperature-dependent susceptibilities of Eu(III). The magnetic susceptibility of the Gd(III) ion in Gd(DBM)3(phen) was identical to that of the free Gd(III) ion, wheras that of the Gd(III) ion in Cs[Eu(DBM)4] was higher. The phen ligand with the π-conjugate rigid planar structure decreased the magnetic susceptibilities of the Eu(III) and Gd(III) ions.

Distinct structural and optical correlations of Y1−xEuxOF and Yn(1−x)EunxOn−1Fn+2 (x=0.001–0.1, n=6, 7) vernier phosphors

Eu3+ substituted YOF and vernier-phase YnOn−1Fn+2 (n=6, 7) phosphors, which are rhombohedral and orthorhombic structures, respectively, were prepared using a flux-assisted reaction at different temperatures. Stoichiometric and nonstoichiometric yttrium oxyfluoride phases were identified by examination of the indexed peak positions in the X-ray diffraction patterns of the resultant phosphors; however, Y6O5F8 and Y7O6F9 lattice structures in vernier phases were indistinguishable by this method. To identify the vernier phases, the photoluminescence excitation and emission spectra peaks assigned to charge-transfer bands and f–f transitions of Eu3+ ions in YnOn−1Fn+2 host with the YOF were monitored. The YnOn−1Fn+2 vernier phases were indicated by the O2−(F−)–Eu3+ charge-transfer bands and the site symmetry of Eu3+ emission assigned by 5D0→7F1, 7F2 transitions, and were classified as centrosymmetric Y6O5F8 and noncentrosymmetic Y7O6F9 structures. The critical distances (Rc) in both Y1−xEuxOF and Y6(1−x)Eu6xO5F8 (x=0.001–0.1) lattice structures were calculated by observation of quenching of the relative intensity in the Eu3+ activated red emission.

Effect of calcination temperature on structural and optical properties of europium (III) doped SrO–Y2O3 phosphor

The SrO–Y2O3:Eu3+ phosphor was synthesized by using solution combustion synthesis and calcined at different temperature. The structure and morphology of the as-prepared material were confirmed by using powder X-ray diffraction pattern and scanning electron microscopy respectively. Further, the phosphors were studied for photoluminescence (PL) and ultraviolet spectroscopy (UV–Vis) for optical measurements. The relation in the site symmetry of Eu3+ was correlated by red to orange ratio, which changes with different calcination temperature. Moreover, the PL spectra shows that there is shifting towards the longer wavelength region with increasing calcination temperature.

Doping concentration induced phase transition in Eu^3+-doped β-PbF_2 nano-particles

Europium doped β-PbF₂ nano-particles with different doping concentration are prepared to investigate the site structure of Eu³⁺ dopants. It is concluded that the site symmetry of Eu³⁺ dopants in β-PbF₂ nano-particles lowers from O(h)to D(4h) with the increase of doping concentration. By X-ray diffraction analysis and photoluminescence spectroscopy study, a doping concentration induced phase transition from lowly doped cubic Pb₃EuF₉ to highly doped tetragonal PbEuF₅ is detected. The intermediate phase of moderately doped nano-particles, which contains both phases mentioned above, is observed for the first time. Moreover, the temperature-dependent intermediate phase analysis suggests that the tetragonal phase is more stable than the cubic phase, which is also confirmed by the first-principle calculations. Our results suggest that the doping concentration induced phase transition in β-PbF₂ nano-particles can be used for understanding other Lanthanide-doped nano-particle systems.

Characterization and optical properties of ZnGa 2O 4:Eu 3+ nanophosphor grown by hydrothermal method

ZnGa 2O 4 phosphor doped with Eu 3+ ions was synthesized by hydrothermal method using two concentrations: 3.34 mol% and 1.67 mol% of Eu 3+. The crystal structure was investigated by means of X-ray diffraction, scanning electron microscopy and atomic force microscopy. The results indicate that the material consisting of ZnGa 2O 4:Eu 3+ nanoparticles exhibits good crystalinity, with cubic spinel structure. The powders were found to have 4.74 eV of ZnGa 2O 4:Eu 3+ (3.34 mol%) and 4.69 eV of ZnGa 2O 4:Eu 3+ (1.67 mol%) band gaps, respectively. The luminescent analysis of the materials shows that the trivalent europium ions doped in this material are localized in different sites, substituting both Zn 2+ and Ga 3+. The emission spectra of the europium-doped samples, originating from 5D 0– 7F J ( J = 0–4) transitions, suggests the existence of three different site symmetry of Eu 3+ ions, tetrahedral (Zn 2+), distorted octahedral (Ga 3+) and low octahedral (Ga 3+) sites, respectively.

High pressure behavior of ZrGeO4: A Raman spectroscopic and photoluminescence study

High pressure behavior of ZrGeO4 has been investigated using Raman and photoluminescence (PL) spectroscopies up to 25 GPa in a diamond anvil cell. Under the application of pressure, the GeO4 librational mode exhibits softening, suggesting dynamical instability of the scheelite structure. Qualitative changes are noted in the Raman spectrum above 12 GPa, suggesting a possible transition around this pressure. High pressure PL behavior of Eu3+-related crystal field transitions indicates a clear change in the site symmetry of Eu3+ around 12 GPa, strongly supporting structural transition to a lower symmetry phase at this pressure.

Crystal growth and magnetic properties of tin selenide-doped europium Sn 1−xEu xSe

The growth and magnetic properties of Tin Selenide (SnSe) doped with Eu 2+ Sn 1− x Eu x Se ( x=2.5%) were investigated. Q-band (34 GHz) electron paramagnetic resonance measurements show that the site symmetry of Eu 2+ at 4.2 K is orthorhombic and the Landé factor was determined to be g=1.99±0.01. The exchange coupling between nearest-neighbor (NN) Eu 2+ ions was estimated from magnetization and magnetic-susceptibility measurements using a model that takes into account the magnetic contributions of single ions, pairs and triplets. The exchange interaction between Eu 2+ nearest neighbors was found to be antiferromagnetic with an estimated average value of J p / k B =−0.18±0.03 K.

Optical Spectroscopy of Eu3+ Doped ZnO Nanocrystals

The energy levels and local structures of Eu 3+ incorporated in the lattice and surface sites of ZnO nanocrystals were investigated based on the high-resolution fluorescence spectra at 10 K. Radiative emissions from 5 D1 were first observed for Eu 3+ at the lattice site of ZnO. It is shown that the site symmetry of Eu 3+ at the lattice site descends from C3V to Cs or C1, whereas Eu 3+ ions at the surface occupy more disordered sites of the lowest symmetry C1. The luminescence decay of 5 D0 at the lattice site, showing a rise time and longer lifetime, behaves distinctly from that of the surface sites. Because of a small filling factor (52%) of nanoparticles, the 5 D0 lifetime of Eu 3+ is significantly affected by the surrounding medium, which can be well interpreted with the virtual-cavity model. The Judd-Ofelt intensity parameters of Eu 3+ in ZnO nanocrystals were determined, with ?2,4,6 values of (9.59, 8.11, <0.25) and (21.51, 2.30, <0.25) in units of 10 -20 cm 2 for Eu 3+ at the surface and lattice sites, respectively. A defect-mediated energy transfer from the ZnO band gap to Eu 3+ was observed. The growth mechanism for the incorporation of Eu 3+ into the ZnO lattice was also revealed.

Organized Nanostructured Complexes of Polyoxometalates and Surfactants that Exhibit Photoluminescence and Electrochromism

AbstractA variety of functional nanostructured organic/inorganic hybrid materials from the europium‐exchanged derivative of a Preyssler‐type polyoxometalate (POM), [EuP5W30O110]12−, and functional organic surfactants were prepared by the ionic self‐assembly (ISA) route. The effect of organic surfactants on the structure, photoluminescent, electrochemical and electrochromic properties of the POM anions was investigated in detail. All obtained hybrid materials are amphotropic, i.e., exhibit both thermotropic and lyotropic liquid‐crystalline phase behaviour. Investigations of their photophysical properties have shown that the interactions of the various surfactants with the polyanions influence the coordination environments and site symmetry of Eu3+ in different ways. The functional groups in the organic surfactants significantly influence the electrochromic properties and photoluminescence of POMs. Different from normal and pyridine‐containing complexes, no photoluminescence and no electrochromism were observed from the ferrocene‐containing complexes. This may be explained in view of charge transfer between the POM anion and the ferrocenyl group.

Optical Spectroscopy of Eu3+ Doped ZnO Nanocrystals

The energy levels and local structures of Eu3+ incorporated in the lattice and surface sites of ZnO nanocrystals were investigated based on the high-resolution fluorescence spectra at 10 K. Radiative emissions from 5D1 were first observed for Eu3+ at the lattice site of ZnO. It is shown that the site symmetry of Eu3+ at the lattice site descends from C3v to Cs or C1, whereas Eu3+ ions at the surface occupy more disordered sites of the lowest symmetry C1. The luminescence decay of 5D0 at the lattice site, showing a rise time and longer lifetime, behaves distinctly from that of the surface sites. Because of a small filling factor (52%) of nanoparticles, the 5D0 lifetime of Eu3+ is significantly affected by the surrounding medium, which can be well interpreted with the virtual-cavity model. The Judd−Ofelt intensity parameters of Eu3+ in ZnO nanocrystals were determined, with Ω2,4,6 values of (9.59, 8.11, <0.25) and (21.51, 2.30, <0.25) in units of 10-20 cm2 for Eu3+ at the surface and lattice sites, respecti...

Influence of different site symmetries of Eu 3+ centers on the luminescence properties of Anderson-based compounds

Two compounds, [Eu(H 2O) 7][Al(OH) 6Mo 6O 18] · 4H 2O ( 1) and {(C 2H 5NO 2) 2[Eu(H 2O) 5]}[Al(OH) 6Mo 6O 18] · 10H 2O ( 2), have been synthesized by conventional solution method and determined by single-crystal X-ray diffraction. Compound 1 shows a 1D chain structure built up of alternating Anderson-type polyanions [Al(OH) 6Mo 6O 18] 3− and hydrated rare-earth ions Eu 3+. Compound 2 displays a 3D supramolecular network structure containing 1D sandglass-like channels along c axis, which were occupied by repetitive array of (H 2O) 8 clusters. Extensive hydrogen bonds play an important role in the formation of the 3D structures of 1 and 2. Luminescence measurements reveal that 1 and 2 exhibit intense red and orange fluorescent emission at room temperature, respectively. Origin of the distinct emission can be assigned to the different site symmetries of Eu 3+ centers in the two compounds. These results are consistent with the crystal structures of the two compounds.

On the enhancement of luminescence efficiency of Y 2O 3:Eu 3+ red phosphor by incorporating (Al 3+, B 3+) in the host lattice

Incorporation of trace (Al 3+, B 3+) in Y 2O 3 lattice, causes an enhancement of efficiency of both 5D 0 → 7F 2 luminescence of Eu 3+ and its excitation in Y 2O 3:Eu 3+ red phosphor. Enhancement of excitation remains restricted around the (Eu 3+–O 2−) C-T band. The 5D 0 → 7F 2 decay characteristics and the build-up time of the 5D 0 excited state of Eu 3+ also change due to such incorporation, although the luminescence pattern remains unchanged. The result suggests a change in polarity of the host rather than the site symmetry of Eu 3+ by the hetero-cations. Calculation of the Judd–Ofelt parameters of the 5D 0 → 7F 2 transition of Eu 3+ gives similar results.