Efficient Co-Adsorption and Highly Selective Separation of Cs+ and Sr2+ with a K+-Activated Niobium Germanate by the pH Control

¹³⁷Cs and ⁹⁰Sr are hazardous to ecological environment and human health due to their strong radioactivity, long half-life, and high mobility. However, effective adsorption and separation of Cs⁺ and Sr²⁺ from acidic radioactive wastewater is challenging due to stability issues of material and the strong competition of protons. Herein, a K⁺-activated niobium germanate (K-NGH-1) presents efficient Cs⁺/Sr²⁺ coadsorption and highly selective Cs⁺/Sr²⁺ separation, respectively, under different acidity conditions. In neutral solution, K-NGH-1 exhibits ultrafast adsorption kinetics and high adsorption capacity for both Cs⁺ and Sr²⁺ (q_m^Cs = 182.91 mg g⁻¹; q_m^Sr = 41.62 mg g⁻¹). In 1 M HNO₃ solution, K-NGH-1 still possesses q_m^Cs of 91.40 mg g⁻¹ for Cs⁺ but almost no adsorption for Sr²⁺. Moreover, K-NGH-1 can effectively separate Cs⁺ from 1 M HNO₃ solutions with excess competing Sr²⁺ and Mⁿ⁺ (Mⁿ⁺ = Na⁺, Ca²⁺, Mg²⁺) ions. Thus, efficient separation of Cs⁺ and Sr²⁺ is realized under acidic conditions. Besides, K-NGH-1 shows excellent acid and radiation resistance and recyclability. All the merits above endow K-NGH-1 with the first example of niobium germanates for radionuclides remediation. This work highlights the facile pH control approach towards bifunctional ion exchangers for efficient Cs⁺/Sr²⁺ coadsorption and selective separation.     

Separation of transuranium and transplutonium elements on S-957 sorbent

Sorption of Pu⁴⁺, UO₂²⁺, NpO₂⁺, Am³⁺, and Eu³⁺ ions on S-957 cation exchanger from 2–7 M HNO₃ solutions was studied. The following selectivity series was obtained: Pu⁴⁺ > UO₂²⁺ > NpO₂⁺ > Am³⁺ ≈ Eu³⁺. The static and dynamic capacities of the sorbent for Pu were determined, and the eluent composition for the efficient desorption was chosen. The possibility of separating Pu(IV)-Am(III) and Pu(IV)-Np(V) pairs on the sorbent in the column chromatography mode was demonstrated.     

Sorption of caesium,strontium and europium ions on clay minerals

Batch experiments have been performed to study the sorption and transport properties of Cs⁺, Sr²⁺ and Eu³⁺ on different clay minerals already established to be predominantly kaolinite and montmorillonite. The uptake of these radionuclides increases in the order Cs相似文献   

Sr3Bi(PO4)3:Eu2+, Mn2+: Single-phase and color-tunable phosphors for white-light LEDs

Sr₃Bi(PO₄)₃:Eu²⁺, Sr₃Bi(PO₄)₃:Mn²⁺, and Sr₃Bi(PO₄)₃:Eu²⁺, Mn²⁺ phosphors were synthesized by solid state reaction. The structure and luminescent characteristics were investigated by X-ray powder diffraction and fluorescent spectrophotometer. All samples have the structural type of eulytine. The excitation and emission spectra of Sr₃Bi(PO₄)₃:0.01Eu²⁺ sample show characteristic bands of Eu²⁺ ions. Also, the excitation and emission spectra of Sr₃Bi(PO₄)₃:0.06Mn²⁺ sample show characteristic bands of Mn²⁺ ions. The emission color of Sr₃Bi(PO₄)₃:Eu²⁺, Mn²⁺ sample could be tuned through tuning the co-dopant concentration of Mn²⁺ ions. The decay times for the Eu²⁺ ions decrease with the increase of Mn²⁺ dopant concentration, but the energy transfer efficiency increases with the increase of Mn²⁺ dopant concentration. On the basis of the luminescent spectra and fluorescence decay curves, we confirm that the energy transfer process from the Eu²⁺ to Mn²⁺ ions takes place in the co-doped Sr₃Bi(PO₄)₃ phosphor. Sr₃Bi(PO₄)₃:Eu²⁺, Mn²⁺ sample shows the good thermostability. The emission intensity of the sample at 400 K is about 60% of the value at 300 K. These results show Sr₃Bi(PO₄)₃:Eu²⁺, Mn²⁺ phosphors could be anticipated for UV-pumped white-light-emitting diodes.     

Affinement de la structure cristalline de Eu3S4

The crystal structure of Eu₃S₄, type Th₃P₄, was refined, on single crystal data, to a R value of 0.026. Only one site may be attributed to europium, accordingly the Eu²⁺ and Eu³⁺ ions are not differentiated.     

Tuning the luminescence color and enhancement of afterglow properties of Sr(4−x−y)CaxBayAl14O25:Eu,Dy phosphor by adjusting the composition

Color point tuning is an important challenge for improving the practical applications of various displays, especially there are very limited white color single hosts that emits in the white spectrum. In this paper, the possibility of color tuning by substituting part of host lattice cation (Sr²⁺ ions) by Ca²⁺ or Ba²⁺ ions in an efficient strontium aluminate phosphor, Sr₄Al₁₄O₂₅:Eu²⁺,Dy³⁺, is reported and found to be very promising for displays. A detail study by replacing part of Sr²⁺ with Ca²⁺ or Ba²⁺ has been investigated. X-ray diffraction study showed that crystal structure of Sr₄Al₁₄O₂₅ is preserved up to 20 mol of Ca²⁺ ion exchange while it is limited to 10 mol of Ba²⁺ ions exchange. Substantial shift in the emission band and color were observed by substitution of Sr²⁺ by Ca²⁺ or Ba²⁺ ions. A bluish-white emission and afterglow was observed at higher Ca²⁺ ions substitution. Further, partial Ca²⁺ substitutions (up to 0.8 mol) resulted in enhanced afterglow of Sr₄Al₁₄O₂₅:Eu²⁺,Dy³⁺ phosphor. However, Ba²⁺ substitution decreased the fluorescence as well afterglow of the Sr₄Al₁₄O₂₅:Eu²⁺,Dy³⁺ phosphor significantly. The enhanced phosphorescence by partial Ca²⁺ substitution is explained on the basis of increased density of shallow traps associated with higher solubility of Dy³⁺ ions in to the host lattice due to equivalent size of Ca²⁺ and Dy³⁺ ions. Thus, Ca²⁺ substitution in the Sr₄Al₁₄O₂₅:Eu²⁺,Dy³⁺ phosphor is a promising method for tuning the emission color and improving the afterglow intensity of the phosphor.     

Effects of Zn doping on the structural and luminescent properties of Sr4Si3O8Cl4:Eu phosphors

Sr₄Si₃O₈Cl₄: Eu²⁺ phosphors were synthesized by the solid-reaction at high temperature. The emission intensity reaches a maximum at 0.08 mol% of Eu²⁺ concentration. The present paper mainly focused on the effects of Zn²⁺ on the crystallization behavior and photoluminescence (PL) properties of Sr₄Si₃O₈Cl₄:0.08Eu²⁺. Results suggested that no new phase is introduced by co-doping with a small amount of Zn²⁺ ions, but when co-doped with excessive amount of Zn²⁺ ions, Sr₂ZnSi₂O₇ appears. We find that the co-doping of a small amount of Zn²⁺ could remarkably improve the PL intensity of Sr₄Si₃O₈Cl₄:0.08Eu²⁺. When x = 0.05, the intensity of Sr₄Si₃O₈Cl₄:0.08Eu²⁺,xZn²⁺ was increased up to 2.3 times that of pure Sr₄Si₃O₈Cl₄:0.08Eu²⁺, which could be attributed to the flux effect of Zn²⁺ ions, and the Zn²⁺ doping reduces the opportunities of the energy transfer between Eu²⁺.     

Ionic Composition of Hot Particles Containing U,Cs, and Sr,Evaluated from the Parameters of X-ray Photoelectron Spectra of Outer U5f and Inner U4f,Cs3d, 4d,and Sr 3d Electrons

The elemental and ionic composition of pellets produced from reactor fuel (UO₂) containing 0.1 wt % Cs and 0.5 wt % Sr relative to U and also of hot particles generated by heating of the fuel to 2000°C and then subjected to additional heating to 900°C in air or argon and condensed on aluminum support was analyzed by the X-ray photoelectron spectroscopy. It was shown that within the first 20 s of heating U and Cs sublime predominantly. In the subsequent 300 s of heating U, Cs, and Sr sublime. For example, it was found that hot particles collected in the first 20 s of heating and subjected to additional heating at 900°C in air flow contain 68% U and 32% Cs, whereas particles collected in the subsequent 360 s and subjected to the same additional heating contain 51% U, 13% Cs, and 36% Sr. It is assumed that these hot particles incorporate uranyl compounds of the following types: UO₂CO₃, Cs₂UO₄, Cs₄UO₂(CO₃)₃, CsUO₂(OH)₃, SrUO₄, Sr₃UO₆, and SrUO₂CO₃(OH)₂. Treatment of the surface of hot particles with Ar⁺ ions produces changes in their composition.     

Luminescent properties of Sr2Al2SiO7:Ce3+,Eu2+ phosphors for near UV-excited white light-emitting diodes

The Sr₂Al₂SiO₇:Eu²⁺, Ce³⁺ phosphors were synthesized by a high temperature solid-state reaction. Effective energy transfer occurs in Ce³⁺ and Eu²⁺ co-doped Sr₂Al₂SiO₇ due to large spectral overlap between the emission of Ce³⁺ and excitation of Eu²⁺ ions. Co-doping of Ce³⁺ enhances the emission intensity of Eu²⁺ greatly by transferring its excitation energy to Eu²⁺ ions. The critical distance has been estimated to be about 1.83 nm by spectral overlap method. Furthermore, the developed phosphors can generate lights from blue to green region under the excitation of UV radiation by appropriately tuning the activator content. The Sr₂Al₂SiO₇:Eu²⁺,Ce³⁺ phosphors are promising phosphors for warm-white-light-emitting diode because of its effective excitation in the near ultraviolet range.     

Structure and luminescence properties of Eu/Tb codoped oxyfluoride glass ceramics containing Sr2GdF7 nanocrystals

Eu/Tb codoped transparent oxyfluoride borosilicate glass ceramics containing Sr₂GdF₇ nanocrystals were fabricated under a reductive atmosphere and the conversion of Eu³⁺ ions to Eu²⁺ ions was observed. The Sr₂GdF₇ nanocrystals with an average size of 32 nm were homogeneously precipitated in the oxyfluoride borosilicate glass matrix, which could be evidenced by X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy-dispersive X-ray (EDX) spectroscopy. The enhancement of photoluminescence emission intensity, reduction of the relative emission intensities between ⁵D₀ → ⁷F₂ and ⁵D₀ → ⁷F₁, and long fluorescence lifetimes of Eu²⁺, Eu³⁺, and Tb³⁺ ions revealed that more rare earth ions were partitioned into the low phonon energy environment Sr₂GdF₇ nanocrystals. Under ultraviolet excitation, pure and bright white light emission was obtained in the oxyfluoride borosilicate glass ceramic, which may be a potential blue, green and red-emitting phosphor for white LEDs.     

Luminescence properties of double-perovskite Sr2Ca1?2xEuxNaxMoO6 red-emitting phosphors prepared by the citric acid-assisted sol–gel method

Double-perovskite Sr₂Ca_1−2x Eu _x Na _x MoO₆ red-emitting phosphors were prepared by the citric acid-assisted sol–gel method, and their luminescence properties were investigated as a function of sintering temperature and Eu³⁺-doping concentration. B-site substituted Sr₂Ca_0.8Eu_0.1Na_0.1MoO₆ phosphor, in which Na⁺ ions act as charge compensators, was selected to study the thermal behavior, phase structure, microstructure, and photoluminescence property under different sintering temperatures. The photoluminescence studies on Sr₂Ca_1−2x Eu _x Na _x MoO₆ (x = 0.02, 0.05, 0.10, 0.15, 0.2) show that a dominant red emission line at around 594 nm, which is due to the Eu³⁺ magnetic dipole transition of ⁵D₀–⁷F₁, is observed under different Eu³⁺ excitations (396 and 412 nm). Further, Eu³⁺ dopant content dependent emission spectra investigations of Sr₂Ca_1−2x Eu _x Na _x MoO₆ phosphors indicates that, when the Eu³⁺ concentrations x = 0.05, there are minimum differences between the emission intensity of ⁵D₀–⁷F₁ transition at 594 nm and that of ⁵D₀–⁷F₂ transition at 615 nm. With increasing Eu³⁺ concentration, the variation of the emission intensities between the two transitions keep nearly invariable and Sr₂Ca_0.8Eu_0.1Na_0.1MoO₆ phosphor has the strongest red emission in this series.     

A novel green-emitting phosphor of Eu2+-doped Cs2MgSi5O12

A new phosphor of Eu²⁺-doped Cs₂MgSi₅O₁₂ was synthesized by conventional solid-state reaction. The phase formation was confirmed by X-ray powder diffraction measurements. The photoluminescence excitation and emission spectra were measured. The phosphor presents bright yellowish-green-emitting luminescence. The site-occupancy of Eu²⁺ ions doped in Cs₂MgSi₅O₁₂ was discussed according to the crystal structure and the luminescence characteristics of Eu²⁺ ions. Two different Eu²⁺ centers were assigned in Cs₂MgSi₅O₁₂ lattices. The dependence of luminescence intensity on the heating temperatures was measured and discussed. The chromaticity coordinates and activation energy (ΔE) for the thermal quenching of Cs₂MgSi₅O₁₂:Eu²⁺ were reported.     

Entrapped Molecule-Like Europium-Oxide Clusters in Zinc Oxide with Nearly Unaffected Host Structure

Nanocrystalline ZnO sponges doped with 5 mol% EuO_1.5 are obtained by heating metal–salt complex based precursor pastes at 200–900 °C for 3 min. X-ray diffraction, transmission electron microscopy, and extended X-ray absorption fine structure (EXAFS) show that phase separation into ZnO:Eu and c-Eu₂O₃ takes place upon heating at 700 °C or higher. The unit cell of the clean oxide made at 600 °C shows only ≈0.4% volume increase versus undoped ZnO, and EXAFS shows a ZnO local structure that is little affected by the Eu-doping and an average Eu³⁺ ion coordination number of ≈5.2. Comparisons of 23 density functional theory-generated structures having differently sized Eu-oxide clusters embedded in ZnO identify three structures with four or eight Eu atoms as the most energetically favorable. These clusters exhibit the smallest volume increase compared to undoped ZnO and Eu coordination numbers of 5.2–5.5, all in excellent agreement with experimental data. ZnO defect states are crucial for efficient Eu³⁺ excitation, while c-Eu₂O₃ phase separation results in loss of the characteristic Eu³⁺ photoluminescence. The formation of molecule-like Eu-oxide clusters, entrapped in ZnO, proposed here, may help in understanding the nature of the unexpected high doping levels of lanthanide ions in ZnO that occur virtually without significant change in ZnO unit cell dimensions.     

Color tunable Sr2SiO4:Eu2+ phosphors through the modification of crystal structure

Eu²⁺ doped Sr₂SiO₄ phosphors were prepared through a solid-state reaction method. The phase-composition and photoluminescence of the obtained phosphors were systematically studied in terms of calcination temperature, Eu and Ba doping. High calcination temperature promoted the phase transformation from α′–Sr₂SiO₄ (orthorhombic) to β–Sr₂SiO₄ (monoclinic), while the doping of Eu or Ba ions could stabilize α′–Sr₂SiO₄ phase due to their long bond length with oxygen. Small amount of Eu/Ba doping prefers to occupy Sr(I) sites in the crystal lattice of Sr₂SiO₄, acting as nucleation sites for both α′– and β–Sr₂SiO₄ phases. After nucleation, Eu²⁺ ions distribute equally in the two sites. Through structural modification, the Sr₂SiO₄:Eu²⁺ phosphors could be controlled to emit different colors in a wide range, from blue to yellow, making them good candidates for tuning the chromaticity in application.     

Sensitization and radiation hardening of the photostimulable X-ray storage phosphor CsBr:Eu2+

The X-ray storage phosphor CsBr:Eu²⁺ in form of needle image plates is believed to be a promising alternative to the granular BaFBr:Eu²⁺ with regard to PSL yield and spatial resolution. Unfortunately, CsBr:Eu²⁺ exhibits poor radiation hardness, which is caused by a migration of europium ions initiated by naturally existing defect centers like (Eu²⁺-V_Cs)-centers and X-ray generated M_Eu-centers. It will be shown that the formation of (Eu²⁺-O²⁻)-dipoles at the expense of (Eu²⁺-V_Cs)-dipoles, incorporated by thermal annealing in O₂-containing and humid atmosphere, does not improve the radiation stability. There is, however, a strong improvement in the radiation hardness by codoping of CsBr:Eu²⁺ with lithium ions, which is accompanied by a complete suppression of the previously observed M_Eu-center formation.     

Effects of RE3+ as a co-dopant in blue-emitting long-lasting phosphors, Sr3Al10SiO20:Eu2+

A series of novel long-lasting phosphors, Sr₃Al₁₀SiO₂₀:Eu²⁺,RE³⁺, were prepared and studied. Under UV irradiation, broad-band emission long-lasting phosphorescence located at 466 nm was observed in all of these phosphors at room temperature. The effects of RE³⁺ as a co-dopant in Sr₃Al₁₀SiO₂₀:Eu²⁺ were discussed in conjunction with the afterglow decay curves and thermoluminescence (TL) spectra. Quantitative TL spectra revealed that the introduction of RE³⁺ ions into Sr₃Al₁₀SiO₂₀:Eu²⁺ host produces a highly dense trapping level at appropriate depth (335 K), which is considered to be responsible for the long-lasting phosphorescence at room temperature.     

Sensitization and radiation hardening of the photostimulable X-ray storage phosphor CsBr:Eu<Superscript>2+</Superscript>

The X-ray storage phosphor CsBr:Eu²⁺ in form of needle image plates is believed to be a promising alternative to the granular BaFBr:Eu²⁺ with regard to PSL yield and spatial resolution. Unfortunately, CsBr:Eu²⁺ exhibits poor radiation hardness, which is caused by a migration of europium ions initiated by naturally existing defect centers like (Eu²⁺-V_Cs)-centers and X-ray generated M_Eu-centers. It will be shown that the formation of (Eu²⁺-O^2?)-dipoles at the expense of (Eu²⁺-V_Cs)-dipoles, incorporated by thermal annealing in O₂-containing and humid atmosphere, does not improve the radiation stability. There is, however, a strong improvement in the radiation hardness by codoping of CsBr:Eu²⁺ with lithium ions, which is accompanied by a complete suppression of the previously observed M_Eu-center formation.     

Synthesis and luminescent properties of Sr<Subscript>4</Subscript>Al<Subscript>14</Subscript>O<Subscript>25</Subscript>:Eu<Superscript>2+</Superscript> blue–green emitting phosphor for white light-emitting diodes (LEDs)

An efficient blue–green emitting phosphor, Sr₄Al₁₄O₂₅:Eu²⁺, was prepared by solid-state reaction. X-ray powder diffraction (XRD) analysis confirmed the formation of Sr₄Al₁₄O₂₅:Eu²⁺. Field-emission scanning electron-microscopy (FE-SEM) observation indicated that the microstructure of the phosphor consisted of irregular fine grains with an average size of about 8–10 μm. Photoluminescence measurements showed a broad absorption band between 300 and 450 nm which was efficiently excited by near-ultraviolet (NUV) LEDs (350–410 nm) and a strong emission band peaking at 491 nm. A bright blue–green LED with chromatic coordination (0.176, 0.412) was fabricated by incorporating the phosphor with an InGaN-based NUV chip, which indicates that Sr₄Al₁₄O₂₅:Eu²⁺ is a good candidate phosphor for application in white LEDs.     

Study on the emission properties of Sr2MgSi2O7:Eu,Dy for luminous fiber application

Rare earth long afterglow phosphors Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ was synthesized by a modified solid-state reaction using H₃BO₃ as auxiliary reagents. In order to promote the emission properties of Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺, samples of Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ were prepared and the effect of manufacturing elements including the concentration of H₃BO₃ and environmental factor of calcining temperature, concentration of Eu²⁺ and Dy³⁺ ions, external environmental factors of applications such as fiber-forming polymer as well as the addition of Ca²⁺ ion on its emission property were investigated through evaluating their emission spectra. The results showed that the molar ratio of the Eu²⁺ ions and Dy³⁺ ions, the amount of doping H₃BO₃, calcining temperature and fiber-forming polymer had little effect on the position of the emission peak and the shape in the luminescence, but greatly influenced the emission intensity of luminescent materials. The effect of Ca²⁺ ion doping was further studied. Ca²⁺ influenced not only the intensity but also the wavelength of emission and spectra of the emission peak shifted to longer wavelength as the concentration of Ca²⁺ increased.     

Luminescence enhancement of Tb3+ in Sr3SiO5:Eu2+ phosphor

Sr₃SiO₅ phosphors co-doped with Eu²⁺ and Tb³⁺ were prepared by a conventional solid-state reaction method. The prepared Sr₃SiO₅:Eu²⁺,Tb³⁺,Li⁺ phosphors had characteristic luminescent spectra excited under near-UV excitation in which both the broadband spectrum assigned to Eu²⁺ and the line spectrum assigned to Tb³⁺ are observed, although Tb³⁺ is inactive with this photon energy in general. For Eu²⁺–Tb³⁺ codoped Sr₃SiO₅, energy transfer process takes place and the mechanism is ascribed to the overlap between the shorter Eu²⁺ luminescence band from the Sr₃SiO₅ crystal structure with two Sr sites and ₅D⁴ energy level of Tb³⁺ ion. Due to the energy transfer, PL intensity of Eu²⁺ emission increased about 26 %. We suggest that this enhancement mechanism could shed light on the potential applications in white light-emitting diodes excited by near-UV light. In addition, the emission peak position near the orange region indicates that our system is a step towards a new class of wavelength sources for artificial lighting with improved PL intensity and lower energy consumption.