In situ analysis for spontaneous reduction of Eu<Superscript>3+</Superscript> in LiCl pyroprocessing media at 923 K

The spontaneous reduction of Eu³⁺ to Eu²⁺ was examined when EuCl₃ was added into a pyroprocessing media of LiCl molten salt at 923 K. The amount of Eu²⁺ was calculated by measuring the total charge consumed to oxidize Eu²⁺ ions to Eu³⁺ ions. The concentration ratio of Eu²⁺ to Eu³⁺ was estimated to be about 0.40 in the media. In addition, it is confirmed that the reduction of Eu³⁺ to Eu²⁺ is caused by the oxidation power of Cl⁻ to Cl₂. The coexistence of Eu³⁺ and Eu²⁺ in the LiCl molten salt system was examined by UV–Visible and luminescence spectroscopy. The molar absorptivities of Eu³⁺ and Eu²⁺, calculated from UV–Visible absorption spectra, were 423 and 1954 M⁻¹ cm⁻¹, respectively.     

Eu<Superscript>3+</Superscript>-fluorescence properties in nano-crystallized SnO<Subscript>2</Subscript>-SiO<Subscript>2</Subscript> glass-ceramics

Fluorescence and spectral hole burning properties of Eu³⁺ ions were studied in nanocrystals-precipitated SnO₂-SiO₂ glasses. The glasses were prepared to contain various amount of Eu₂O₃ using the sol-gel method, in which SnO₂ nanocrystals were precipitated by heating in air. In the glasses containing Eu₂O₃ less than 1%, the Eu³⁺ ions were preferentially doped in the SnO₂ nanocrystals and their fluorescence intensities were enhanced by the energy transfer due to the recombination of electrons and holes excited in SnO₂ crystals. The SnO₂ nanocrystals-precipitated glasses exhibited the persistent spectral holes with the depth of ∼25% of the total fluorescence intensities of the Eu³⁺ ions. With the increasing Eu₂O₃ concentration, the amount of SnO₂ nanocrystals decreased and the Sn⁴⁺ ions formed the random glass structure together with the silica network. This structure change induced the fluorescence intensities and the hole depth to decrease.     

High sensitivity and multicolor tunable optical thermometry in Bi3+/Eu3+ co-doped Ca2Sb2O7 phosphors

Currently, with increasing demand for non-contact fluorescence intensity ratio-based optical thermometry, a novel phosphor with high-efficiency, dual-emitting centers, and differentiable temperature sensitivity is more and more urgent to develop. In this work, an efficient dual-emitting center optical thermometry with high sensitivity and multicolor tunable in Ca₂Sb₂O₇:Bi³⁺, Eu³⁺ phosphor is firstly designed and successfully prepared. Under 330 nm excitation, the fabricated phosphor presents the featured and distinguishable emissions of Bi³⁺ and Eu³⁺ ions. The high efficiency energy transfer from Bi³⁺ to Eu³⁺ ions is proved and its corresponding mechanism belongs to dipole-dipole interaction. By modulating the ratio of Bi³⁺/Eu³⁺, the multicolor changes from blue to pink are realized. Based on the discriminative thermal quenching behavior between Bi³⁺ and Eu³⁺, the fluorescence intensity ratio of Eu³⁺ to Bi³⁺ in Ca₂Sb₂O₇ samples illustrates excellent optical thermometry performance from 298 to 523 K. The maximum absolute sensitivity (S_a) and relative sensitivity (S_r) reach as high as 0.2773 K^?1 at 523 K and 2.37% K^?1 at 448 K, respectively. Notably, the discriminated surrounding temperature can be directly confirmed by observing the emitting color from purple to orange-red with the temperature increase from 298 to 523 K. Furthermore, the as-prepared phosphor materials also demonstrate outstanding repeatability and excellent reversibility. These results exhibit that the designed Ca₂Sb₂O₇:Bi³⁺, Eu³⁺ phosphors have great promising applications in the field of non-contact optical temperature thermometry and thermochromic.     

Energy transfer between Eu2+ ions in RbMgF3 crystals

Time-resolved spectroscopy after pulsed nitrogen laser excitation was used to characterize the energy transfer between Eu²⁺ ions in different crystal field sites in RbMgF₃ crystals. The results are consistent with electric dipole—dipole interaction and indicate that the Eu²⁺ ions are forming clusters in this host. As temperature is raised, the upper crystal field components of the metastable states of the ions become thermally populated and this changes the characteristics of the transfer process.     

Photoreduction of Europium (III) in Sol-Gel Derived Inorganic-Organic Hybrid Materials

Eu²⁺-doped inorganic-organic hybrid materials, which are potentially suitable for a tunable laser in the near ultra violet and blue region, were prepared through the photoreduction of Eu³⁺ ions in the materials under the irradiation of the fourth harmonic wave light (266 nm) of the Nd:YAG laser. The hybrid materials doped with Eu³⁺ ions were prepared from Si(OCH₃)₄, CH₃Si(OCH₃)₃, EuCl₃ and chloropropyltrimethoxysilane (CPTM). After the prehydrolized silica sol was added to the Eu³⁺-containing solution, Eu³⁺-doped transparent inorganic-organic hybrid material was obtained by drying at 50°C. The emission peak around 450–475 nm due to the charge transfer transition (5d-4f) of Eu²⁺ ions increased with the laser irradiation time. Eu³⁺ ions were effectively photoreduced to Eu²⁺ ions in pore-free materials prepared at high CPTM to Eu³⁺ ratios. Eu²⁺ ions were generated by the photodecomposition of the bond between Eu³⁺ and Cl (Cl^– or Cl(CH₂)₃ in CPTM).     

Luminescence and energy transfer in a highly symmetrical system: Eu2Ti2O7

Luminescence and energy transfer properties of Gd₂Ti₂O₇: Eu and Eu₂Ti₂O₇ are reported. Transfer between unperturbed (intrinsic) Eu³⁺ ions and perturbed (extrinsic) Eu³⁺ ions has been observed. At low temperatures the emission spectra of Eu₂Ti₂O₇ are dominated by trap emission, due to direct energy transfer from the intrinsic Eu³⁺ ions to the extrinsic Eu³⁺ ions. Above 10 K energy migration among the Eu³⁺ ions to quenching centers occurs. The interaction between the Eu³⁺ ions is probably exchange in character. The nature of the extrinsic Eu³⁺ ions has been elucidated.     

Intercalation of cytosine into Eu<Superscript>3+</Superscript>-doped hydrocalumite and their fluorescent responses

Intercalation of cytosine into Eu³⁺-doped hydrocalumites and the fluorescence of the Eu³⁺-doped hydrocalumite response to cytosine has been investigated. XRD patterns showed that the basal spacing of Eu-doped hydrocalumite obviously increased after it exposed to various content of cytosine, revealing the intercalation of cytosine into Eu³⁺-doped hydrocalumite. TG-DSC curves and IR spectra of the intercalated samples are different from that of the Eu-doped hydrocalumite and cytosine, indicating the interaction between the Eu³⁺-doped hydrocalumite and cytosine. Fluorescent spectra suggested that the fluorescent changes of Eu³⁺-doped hydrocalumite depended on the concentration of cytosine solution. This fluorescent change would be potential application in biological probe in view of the biocompatibility of Ca²⁺ ions and the fluorescence of Eu³⁺ ions. Moreover, the Eu³⁺-doped hydrocalumite would be a healthy and cheap fluorescent material applied in biology or healing drugs fields.     

Ultraviolet 5H3 and visible 5DJ luminescence of europium(III)co-doped with cerium (III) in hexagonal NaGdF4

The luminescence of NaGdF₄:Ce,Eu has been investigated. After excitation of Ce³⁺ ions at room temperature, energy transfer to the Gd³⁺ions occurs, followed by migration over this sublattice to the Eu³⁺ions, resulting mainly in Eu³⁺ emission. At liquidhelium temperatures mainly Gd³⁺⁶P trap emission is observed. The Eu³⁺ emission in this system is remarkable, because ultraviolet Eu³⁺ emission (⁵H₃-⁷F_J) is observed alongside the normal ⁵D_J emission in the visible region.     

Local structure and photoluminescent characteristics of Eu<Superscript>3+</Superscript> in ZnO–SiO<Subscript>2</Subscript> glasses

The photoluminescence properties of xZnO–(100−x)SiO₂ (x = 0, 5, 10, 20) containing 1% Eu₂O₃ prepared by a sol–gel method were systematically investigated. The results indicated that the relative proportion of f–f transitions to charge transfer (CT) absorption decreased with the increase of ZnO concentration. The intensity of ⁵D₀–⁷F_J transitions of Eu³⁺ ions was enhanced with the increase of ZnO content due to local structure changes and decreased quantities of Eu³⁺ ions clusters. The results of fluorescence line narrow (FLN) spectra indicated that Eu³⁺ ions occupied one site in SiO₂ glass and two sites in ZnO–SiO₂ glasses. The second-order crystal field parameters were calculated. B₂₀ and B₂₂ for site 1 increased with excitation energy, while ones hardly changed for site 2.     

The standard and anomalous crystal-field spectra of Eu

The crystal-field (CF) spectra of Eu³⁺ in various inorganic crystalline phases are summarized based on previous investigations. A majority of experimental results can be well interpreted using a standard CF model. However, there are cases in which the spectroscopic properties and fluorescence dynamics of Eu³⁺ cannot be interpreted within the framework of the standard model. A particularly interesting system is Eu³⁺ doped into microcrystals of a charge-unbalanced host such as BaFCl. For Eu³⁺:BaFCl, one Eu³⁺ site (Site I) exhibits normal CF splitting and its energy levels and fluorescence intensity are similar to most other normal systems ever reported. A standard CF fitting has been performed for Site I. However, Eu³⁺ at a distorted site (Site II) is of anomalous fluorescence dynamics and CF splitting which are significantly different from those of Site I. In the metastable state of ⁵D₀, Eu³⁺ ions at Site II also exhibit unusual temperature-dependent lifetime.     

Magnetic properties and Eu Mössbauer effects of mixed valence europium copper sulfide, Eu2CuS3

Ternary europium copper sulfide Eu₂CuS₃ have been investigated by X-ray diffraction, ¹⁵¹Eu Mössbauer spectroscopy, magnetic susceptibility, magnetization, and specific heat measurements. In this compound, Eu²⁺ and Eu³⁺ ions occupy two crystallographically independent sites. The ¹⁵¹Eu Mössbauer spectra indicate that the Eu²⁺ and Eu³⁺ ions exist in the molar ratio of 1:1, and the Debye temperatures of Eu²⁺ and Eu³⁺ are 180 and 220 K, respectively. In its magnetic susceptibility, the divergence between the zero-field cooled and field cooled susceptibilities appears below 3.4 K. The specific heat has a λ-type anomaly at the same temperature. From the field dependence of magnetization at 1.8 K, the Eu²⁺ ion was found to be in the ferromagnetic state with the saturation magnetization M_S=6.7 μ_B.     

A Logic Fluorescent Chemosensor Based on Eu3+ Functionalized Cd-MOFs for Sensing Fe3+ and Cu2+ Synchronously

One of the most critical and yet unsolved issues is the effective monitoring of multiple heavy metal ions in complex systems through their specific function in fluorescence detection. In this work, luminescence-active cadmium base metal-organic frameworks (Cd-MOFs) based on the planar and rigid π-conjugated structure ligand benzo-(1,2;3,4;5,6)-tris (thiophene-2’-carboxylic acid) (H₃BTTC) was chosen. A series of sensing experiments demonstrated that the Cd-MOFs exhibits selective and sensitive response for Fe³⁺ and Eu³⁺ through fluorescence “turn off” and “antenna effect” respectively. In addition, the encapsulation of Eu³⁺ inside the Cd-MOFs (Eu³⁺@Cd-MOFs) led to an excellent probe with dual emission. To this end, a programmable fluorescence platform was developed to detect Fe³⁺ and Cu²⁺, in which the emission peaks of both the ligand and Eu³⁺ are completely quenched by Fe³⁺. The ratiometric detection of Cu²⁺ leads to a decrease in Eu³⁺ emission, while the ligand emission remains stable. To demonstrate the strategy, the fluorescence (Output) of Cd-MOFs, Eu³⁺@Cd-MOFs, and the analytes (Eu³⁺, Fe³⁺, and Cu²⁺, input) achieved elementary Boolean logic operations (OR, NOR, AND) and they constitute a logic fluorescent chemosensor to analyze Fe³⁺ and Cu²⁺ synchronously.     

Synthesis and Characterization of Europium‐exchanged Titanate Nanoporous Phosphors

Eu_x(NH₄)_2‐2xTi₃O₇ nanoporous phosphor was prepared by ion exchange method. (NH₄)₂Ti₃O₇ nanotubes were employed as the host structure by treating H₂Ti₃O₇ with NH₄OH solution and the activator, Eu²⁺, was introduced into the host via ion exchange. This is an easy and feasible way to prepare a phosphor. The synthesized samples were characterized using TEM, XRD, N₂ adsorption‐desorption isotherm, TPR, and fluorescence spectrophotometer. Experimental results showed that a portion of Eu²⁺ ions was oxidized into Eu³⁺ ions during ion exchange, resulting in the present phosphor with blue‐emitting and red‐emitting. Moreover, the tubular structure of Eu_x(NH₄)_2‐2xTi₃O₇ was distorted as Eu²⁺ was placed into the host structure. This distortion is attributed to the electrostatic interaction between Eu²⁺ and the electric field of the host structure.     

Effect of SnO2 Nanocrystals on the Emission of Eu3+ Ions in Silica Matrix

Silica xerogels containing Eu³⁺ ions and SnO₂ nanocrystals were prepared in the sol‐gel process, and characterized by x‐ray diffraction (XRD) and photoluminescence spectra. Under the excitation at 393 nm, characteristic emission of Eu³⁺ ions at 614 nm was enhanced with increasing amount of SnO₂ nanocrystals. Moreover, when the Eu³⁺/SnO₂ co‐doped samples were excited at 345 nm, corresponding to the sideband of SnO₂ nanocrystals, the emission of Eu³⁺ ions at 614 nm was clearly observed, while no emission of Eu³⁺ ions for the Eu³⁺‐doped sample. It may be ascribed to the energy transfer from SnO₂ conduction band to Eu³⁺ conduction band. Further experimental results suggest that the energy transfer may be achieved through surface transition state.     

Fluorescence techniques for metal-humic interactions

Summary Two fluorescence techniques to study metal-humic interactions are presented. In the first technique, Lanthanide Ion Probe Spectroscopy (LIPS), the humic samples are titrated by Eu³⁺ ions. The ratio of the intensities of two emission lines of Eu³⁺, R=I₅₉₂/I₆₁₆, is used to estimate the amount of bound and free species of the probe ions. The titration plot is presented as R versus the logarithm of total added Eu³⁺. In the second technique, fluorescence quenching of the humic material by Cu²⁺ is used to produce titration curves of intensity versus the logarithm of total added Cu²⁺. The two techniques are used in conjunction with a model that treats the various ligands in humic substances as continuous distributions of binding sites in which individual ligand concentrations are normally distributed with respect to the individual stability constants for metal binding. The model includes the effects of pH, ionic strength, and competing metal ions. The parameters of the model are estimated by fitting the spectral titration data to the calculated titration plot. Some simulation and experimental data are presented and discussed.     

Photoluminescence Properties of Silica Xerogels Co‐doped with Eu3+ Ions and CdS Nanoparticles

Silica xerogels doped with Eu³⁺ ions and co‐doped with Eu³⁺ ions and CdS nanoparticles were prepared using a two‐step hydrolysis process. The effect of temperature on photoluminescence properties of Eu³⁺‐doped silica xerogel was investigated. The results showed that the photoluminescence of Eu³⁺‐doped silica xerogel was significantly dependent on the temperature of heat treatment. The study of the photoluminescence of co‐doped xerogels showed that the defect emission of silica was weakened due to competition among defects, CdS nanoparticles, and Eu³⁺ ions.     

Two valence states in oxidized europium metal

Evaporated Eu films were exposed to oxygen up to 100 L. Using novel techniques of photoelectron spectroscopy in connection with synchrotron radiation as a tunable light source we detect the presence of both Eu²⁺ and Eu³⁺ ions in the sample with a close correspondence to mixed-valence Eu₃O₄. At elevated temperature (400°C) only Eu²⁺ is found.     

Laser spectroscopic study of multiple Eu3+ sites and their crystal fields in YAlG crystals

Resonance fluorescence spectra are excited from a single crystal of curopium doped yttrium aluminum garnet. An analysis from the energy spectrum shows that the spectra are due to trivalent europuim ions occupying two different sites in the unit cell and a crystal field analysis reveals that these ions at these sites experience fields of orthorhombic and axial symmetry. The former is that expected if Eu³⁺ replaces the Y³⁺ at the orthorhombic d sites, the latter if the lanthanide ion replaces the Al³⁺ ions at the a sites (with a distorted C_3i symmetry), there are indications that Eu³⁺ prefers the a over the d sites.     

Energy Transfer Between Eu3+ Ions and CdS Quantum Dots in Sol-Gel Derived CdS/SiO2 : Eu3+ Gel

We have investigated the energetic correlation between rare-earth ions and semiconductor nanocrystals, using europium ion (Eu³⁺) doped silica (SiO₂) gel with adsorbed cadmium sulfide (CdS) particles. Samples were prepared by a sol-gel technique, in which several methods for the precipitation of CdS colloids were attempted. The fluorescence intensities were compared for different gels, with and without CdS particles. The intrinsic emission lines due to ⁵D₀ ⁷F_J(J = 0–4) transitions of Eu³⁺ were observed, which were enhanced for 24 h-immersed gel (dried at 50°C). From the results on the decay dynamics of fluorescence, we proposed the model that surface-trapped electrons on CdS particles nonradiatively excited 4f electrons in Eu³⁺ ions due to an energy transfer process.     

Luminescence and energy migration characteristics of EuWO4Cl

Luminescence and energy transfer properties of EuWO₄Cl and Gd_0.99Eu_0.01WO₄Cl are reported. Emission due to a small amount of second phase has been observed for both samples. Energy migration among the Eu³⁺ ions has been observed for EuWO₄Cl. The temperature dependence of the migration rate can be explained assuming phonon-assisted energy transfer. The interaction between the Eu³⁺ ions is probably multipole-multipole in character.