Structure, Thermal Stability, and Spectroscopic Properties of Triclinic Double Sulfate AgEu(SO4)2 with Isolated SO4 Groups

Site regulation and luminescence properties of Eu3+, Eu2+ in (La, Mg):SrAl12O19 matrix

The partially and equivalent substitution of La + Mg → Sr + Al in SrAl12O19 lattice is an effective strategy to provide trivalent sites, reduce the site occupation splitting of Al and stabilize the entire lattice. When excited by 397 nm, the Eu3+ activated La, Mg:SrAl12O19 (ASL) phosphor shows intense linear emission through the 5D0→7F4 transition at 707 nm when compared with SrAl12O19:Eu3+. Especially, the Eu, Mg co-doped Sr1-xLaxMgxAl12-xO19 with certain amount of x = 1/3 exhibits the significant intense photoluminescence, which was demonstrated through a lattice evolutional model. Eu2+ in the host with 1/3 ratio of (La, Mg) substitution shows broad blue emission and as short fluorescence lifetime as 248 ns. The temperature-depended fluorescence quenching behavior confirms the essence of strong electric-phonon coupling originated from distorted and polarized crystal field around Eu2+/Sr2+ site. Basing on site regulation of SrAl12O19 matrix, our study provides a reference for exploration on efficient rare earth ions activated luminescent laser or scintillation materials.

Negative Thermal Expansion in the Polymorphic Modification of Double Sulfate β-AEu(SO4)2 (A-Rb+, Cs+)

New polymorphic modifications of double sulfates β-AEu(SO₄)₂ (A-Rb⁺, Cs⁺) were obtained by the hydrothermal method, the structure of which differs significantly from the monoclinic modifications obtained earlier by solid-state methods. According to single-crystal diffraction data, it was found that the compounds crystallize in the orthorhombic system, space group Pnna, with parameters β-RbEu(SO₄)₂: a = 9.4667(4) Å, b = 13.0786(5) Å, c = 5.3760(2) Å, V = 665.61(5) ų; β-CsEu(SO4)2: a = 9.5278(5) Å, b = 13.8385(7) Å, c = 5.3783(3) Å, V = 709.13(7) ų. The asymmetric part of the unit cell contains one-half Rb⁺/Cs⁺ ion, one-half Eu³⁺ ion, both in special sites, and one SO₄^2- ion. Both compounds exhibit nonlinear negative thermal expansion. According to the X-ray structural analysis and theoretical calculations, the polarizing effect of the alkali metal ion has a decisive influence on the demonstration of this phenomenon. Experimental indirect band gaps of β-Rb and β-Cs are 4.05 and 4.11 eV, respectively, while the direct band gaps are 4.48 and 4.54 eV, respectively. The best agreement with theoretical calculations is obtained using the ABINIT package employing PAW pseudopotentials with hybrid PBE0 functional, while norm-conserving pseudopotentials used in the frame of CASTEP code and LCAO approach in the Crystal package gave worse agreement. The properties of alkali ions also significantly affect the luminescent properties of the compounds, which leads to a strong temperature dependence of the intensity of the ⁵D₀ → ⁷F₄ transition in β-CsEu(SO₄)₂ in contrast to much weaker dependence of this kind in β-RbEu(SO₄)₂.

Effect of Dy3+ and Tb3+ Rare-Earth Cation Co-Substitution on the Structure, Magnetic, and Magnetostrictive Properties of Ni-Co-Ferrites

The design and development of electromagnetic and magnetoelectric materials with enhanced properties and performance are desirable for numerous technologies, which are based on integrated electromagnetic materials and components. Nevertheless, engineering the crystalline materials with multi-complex chemistry and multiple cations is challenging. In this context, herein, we report on the effect of rare-earth (RE) cations, namely, Dy³⁺ and Tb³⁺, co-substituted into the Co-Ni-mixed ferrite materials for applications in stress/torque sensors. The RE-cations that co-substituted Co-Ni-ferrite materials with a composition of Ni_0.8Co_0.2Fe_2-x(Dy_1-yTb_y)_xO₄ (x = 0-0.1, y = 0.3; NCFDT) were prepared by the high-temperature solid-state chemical reaction method. The effect of variable composition (x) on the structure, morphology, chemical bonding, and magnetic properties of NCFDT materials is investigated in detail, and the structure-property optimization enabled realizing magnetostrictive NCFDT for sensor applications. X-ray diffraction analysis coupled with Rietveld refinement confirms the face-centered cubic crystal structure. Chemical bonding analysis made using Raman spectroscopic and Fourier transform infrared spectroscopic measurements validates the active modes corresponding to the spinel ferrite structure. The effect of Dy³⁺ and Tb³⁺ substitution is primarily seen in the grain size (range of 5-15 μm), as evident from the scanning electron microscopy patterns. Energy-dispersive spectroscopy confirms the presence of all constituent elements with expected composition and without any impurities. The magnetic property measurements indicate that the remnant magnetization (M_r) increases from 0.06 to 0.17 μ_B/f.u. with the rare-earth (Dy and Tb) substitution and has achieved the maximum squareness ratio (M_r/M_s) = 0.097 at x = 0.10. To validate their application potential in magneto-mechanical sensors, we have measured the magnetostriction coefficients (λ₁₁ and λ₁₂), which demonstrate high values of λ₁₁ = -92 ppm (along the parallel direction) and λ₁₂ = 66 ppm (along the perpendicular direction) for NCFDT with x = 0.05 at H = 7000 Oe. In addition, the maximum value of strain sensitivity is observed, particularly dλ11dH = -0.764 nm/A whereas dλ12dH = 0.361 nm/A. The correlation between strain sensitivity (dλ/dH) and susceptibility (dM/dH), as derived from magnetostriction and magnetization measurements, respectively, is established. The outcomes of this study indicate that Ni-Co-ferrites with Dy³⁺ and Tb³⁺ substitution are suitable for stress/torque sensors. These NCFDT ferrites may also be useful as a necessary constitutive phase for the manufacture of magnetoelectric composite materials, making them appropriate for magnetic field sensors and energy harvesting applications.

Synthesis and Characterization of Coordination Compound [Eu(µ2-OC2H5)(btfa)(NO3)(phen)]2phen with High Luminescence Efficiency

A high-luminescent, blue-light excitable europium(III) coordination complex, [Eu(µ₂-OC₂H₅)(btfa)(NO₃)(phen)]₂phen (1) {btfa = benzoyl trifluoroacetone, phen = 1,10-phenantroline}, has been synthesized and investigated. The complex was characterized by infrared (IR) and photoluminescence (PL) spectroscopy. The PL emission spectra of powder samples registered in a range of 10.7-300 K exhibit characteristic metal-centered luminescence bands, assigned to internal radiative transitions of the Eu³⁺ ion, ⁵D₁→⁷F_j and ⁵D₀→⁷F_j (j = 0-4). The high-resolution spectrum of the transition ⁵D₀→⁷F₀ shows that it consists of two narrow components, separated by 0.96 meV, which indicates the presence in the matrix of two different sites of the Eu³⁺ ion. The splitting pattern of ⁵D₀→⁷F_j (j = 0-4) transitions indicates that europium ions are located in a low-symmetry environment. The absolute quantum yield and the sensitization efficiency were determined to be 49.2% and 89.3%, respectively. The complex can be excited with low-cost lasers at around 405 nm and is attractive for potential applications in optoelectronics and biochemistry.

Designing Optical Thermometers Using Down/Upconversion Ca14Al10Zn6O35: Ti4+, Eu3+/Yb3+, Er3+ Thermosensitive Phosphors

Down/upconversion Ca₁₄Al₁₀Zn₆O₃₅ inorganic phosphors codoped with Ti⁴⁺/Eu³⁺ or Yb³⁺/Er³⁺ were prepared. The crystal structure and downconversion luminescence properties of Ca₁₄Al₁₀Zn₆O₃₅:Ti⁴⁺, Eu³⁺ phosphors were studied in detail. Ti⁴⁺ and Eu³⁺ occupied Al³⁺ and Ca²⁺ sites in the host lattice, respectively. Under the excitation of 273 nm, the emission peak in the 300-570 nm band originated from the ²T₂ → O^2- transition of Ti⁴⁺. The f-f transition of Eu³⁺ ions generated multiple peaks in the 570-800 nm range. The emission intensity of Ti⁴⁺ and Eu³⁺ ions can be used as a fluorescence intensity ratio (FIR) signal. Based on the FIR technology, the maximum relative sensitivity (S_r) and the minimum temperature uncertainty (δT) reached 1.41% K^-1 and 0.07 K, respectively. Meanwhile, the temperature-sensing behaviors were explored by the temperature-dependent upconversion spectra of Er³⁺- and Yb³⁺-codoped Ca₁₄Al₁₀Zn₆O₃₅ phosphors. Based on the fluorescence intensity ratio of thermal coupling levels (Er³⁺:²H_11/2/⁴S_3/2), the maximum S_r and minimum δT of upconversion phosphors reached 1.28% K^-1 and 0.08 K in the temperature range of 293-473 K, respectively. Ca₁₄Al₁₀Zn₆O₃₅:Ti⁴⁺/Eu³⁺ (Yb³⁺/Er³⁺) phosphors realize temperature sensors with higher relative sensitivity, and it is a good candidate material for optical temperature measurement.

Exploration of the Crystal Structure and Thermal and Spectroscopic Properties of Monoclinic Praseodymium Sulfate Pr2(SO4)3

Praseodymium sulfate was obtained by the precipitation method and the crystal structure was determined by Rietveld analysis. Pr2(SO4)3 is crystallized in the monoclinic structure, space group C2/c, with cell parameters a = 21.6052 (4), b = 6.7237 (1) and c = 6.9777 (1) Å, β = 107.9148 (7)°, Z = 4, V = 964.48 (3) Å3 (T = 150 °C). The thermal expansion of Pr2(SO4)3 is strongly anisotropic. As was obtained by XRD measurements, all cell parameters are increased on heating. However, due to a strong increase of the monoclinic angle β, there is a direction of negative thermal expansion. In the argon atmosphere, Pr2(SO4)3 is stable in the temperature range of T = 30-870 °C. The kinetics of the thermal decomposition process of praseodymium sulfate octahydrate Pr2(SO4)3·8H2O was studied as well. The vibrational properties of Pr2(SO4)3 were examined by Raman and Fourier-transform infrared absorption spectroscopy methods. The band gap structure of Pr2(SO4)3 was evaluated by ab initio calculations, and it was found that the valence band top is dominated by the p electrons of oxygen ions, while the conduction band bottom is formed by the d electrons of Pr3+ ions. The exact position of ZPL is determined via PL and PLE spectra at 77 K to be at 481 nm, and that enabled a correct assignment of luminescent bands. The maximum luminescent band in Pr2(SO4)3 belongs to the 3P0 → 3F2 transition at 640 nm.

A new rare-earth oxyborate Ba3BiPbEuO(BO3)4 and the luminescence properties of the Ba3BiPbY1-xEuxO(BO3)4 phosphors

A new rare-earth oxyborate Ba₃BiPbEuO(BO₃)₄ was prepared, and its crystal structure was established by the single-crystal X-ray diffraction method with the following structural data: P6₃/mmc, a = 5.4305(1) Å, c = 26.3501(3) Å, V = 672.96(3) ų and Z = 2. This is a layered material containing two types of layers: one is formed by corner-sharing EuO₆ octahedra and BO₃ triangles and the other is composed of corner- or edge-sharing (Bi/Pb)O₇ hexagonal pyramids and BO₃ triangles. These layers and their equivalent partners are alternately stacked along the c-axis, with Ba²⁺ cations situated in between and within the layers. Furthermore, the phase composition, morphology, and IR, Raman, XPS, and UV-vis absorption spectra of this compound were studied. In addition, solid solutions of Ba₃BiPbY_1-xEu_xO(BO₃)₄ (0 ≤ x ≤ 1) were prepared via the solid-state reaction method and their photoluminescence properties were investigated. Ba₃BiPbYO(BO₃)₄ and Ba₃BiPbEuO(BO₃)₄ showed blue and reddish-orange luminescence when excited at 242 and 394 nm, respectively. By doping Eu³⁺ into the Ba₃BiPbYO(BO₃)₄ matrix and changing the Eu³⁺ doping concentration, luminescence color tunability from blue to orange-red was realized in Ba₃BiPbY_1-xEu_xO(BO₃)₄ phosphors under excitation at 331 nm. This kind of material with color variability may have potential application in field-emission displays.

Regulation of Local Site Structures to Stabilize Mixed-Valence Eu2+/3+ under a Reducing Atmosphere for Multicolor Photoluminescence

Co-doping mixed-valence Eu^2+/3+ in a single-phase phosphor is an efficient method to realize the emission color regulation, which holds great potential for anticounterfeiting and ratiometric temperature sensing. Here, the mixed-valence Eu-doped Sr_1.95+xLi_1-xSi_1-xAl_xO₄F (0 ≤ x ≤ 0.25) phosphors were designed and prepared under a reducing atmosphere. The correlation of local phase structures and luminescence properties was discussed. Replacing Si⁴⁺-Li⁺ ion pairs with Al³⁺-Sr²⁺ ion pairs compresses the Sr sites occupied by Eu²⁺, and it stabilizes Eu³⁺ in a reducing atmosphere and leads to the coexistence of Eu²⁺ and Eu³⁺ in single-phase Sr_1.95+xLi_1-xSi_1-xAl_xO₄F:0.05Eu (0 ≤ x ≤ 0.25) phosphors. Based on the wavelength-dependent luminescence color behaviors of Sr_1.95+xLi_1-xSi_1-xAl_xO₄F:0.05Eu phosphors, the fluorescent anticounterfeit papers/patterns containing Sr_1.95+xLi_1-xSi_1-xAl_xO₄F:0.05Eu phosphors were the same as ordinary paper under ambient conditions. However, the hidden colors or images can be read out with green-orange luminescence under 365/300 nm light excitation. Benefiting from the diverse thermal response emission behaviors of Eu²⁺ (530 nm) and Eu³⁺ (703 nm), Sr_1.95+xLi_1-xSi_1-xAl_xO₄F:0.05Eu phosphors exhibit temperature sensing performances, with the maximum absolute and relative sensitivity being 0.0294 K^-1 at 573 K and 0.83% K^-1 at 348 K. More importantly, Sr_1.95+xLi_1-xSi_1-xAl_xO₄F:0.05Eu phosphors showed excellent stability in humid, acid, and alkali environments, which contributed to applying mixed-valence Eu^2+/3+-doped Sr_1.95+xLi_1-xSi_1-xAl_xO₄F to the fields of multicolor anticounterfeiting and noncontact optical thermometry.

Microwave assisted Synthesis of ZnGa2-x-yEuxTbyO4 luminescent nanoparticles showing balanced white-light emission

Phosphor-converted white-light-emitting diodes (pc-WLED) are technologically advanced next-generation lighting sources which will potentially substitute traditional lighting. Herein, we report microwave-assisted synthesis of single-phase, ZnGa2-x-yEuxTbyO4 nanophosphor in 10 min with high...

Co-crystallization of red emitting (NH4)3Sc(SO4)3:Eu3+ microfibers: structure-luminescence relationship for promising application in optical thermometry

(NH4)3Sc(SO4)3:Eu3+ phosphor has been synthesized as rod-like microparticles by the crystallization from an aqueous solution. Its crystal structure belongs to monoclinic system, space group P21/c, Z = 4. An enantiotropic...

Luminescence properties of Eu2O3-doped ZrO2–Y2O3 single crystals

The optical properties of the Eu3+-doped Y2O3-stabilized ZrO2 crystals demonstrate potential for various applications based on their intense emission of orange light.

Microstructural origin of peculiar spectra and excellent luminescence properties of Y10Ta4O25:Eu3+ with a fluorite-related structure

Y10Ta4O25:Eu3+ presents peculiar spectra and excellent red luminescence properties due to its special fluorite-related structure. The microstructure was characterized by the site-selective luminescence of Eu3+ activators.

Bi3+ photoluminescence in Y1-xBixCa3(GaO)3(BO3)4 and energy transfer to Eu3+ and Tb3+ in co-doped phosphors

Bi³⁺ possesses outer shell lone pair electrons, and, thus the so-involved photoluminescence (PL) is sensitive to the surrounding coordination. Besides, the similarity in the structural chemistry between Bi³⁺ and rare earth (RE) ions inspires us to investigate the Bi³⁺-PL performance in RE³⁺-containing hosts. Herein, Y_1-xBi_xCa₃(GaO)₃(BO₃)₄ (0.01 ≤ x ≤ 0.15) compounds were prepared by a high temperature solid state reaction method. The successful cationic doping and phase purity were confirmed by powder X-ray diffraction analysis. This series of phosphors exhibit the very strong absorption of Bi^{3+ 1}S₀ → ³P₁ at 272 nm along with the intense blue emission with a maximum at 399 nm and a full width at half maximum (FWHM) of 59 nm. They retained 78.86% of the emission intensity at 150 °C, with reference to that at room temperature. Moreover, Bi³⁺ could also behave as a sensitizer to enhance the emission efficiency of RE³⁺ and thus to realize color-tunable phosphors. The energy transfer was proved in the co-doped phosphors Y_0.95-yBi_0.05Eu_yCa₃(GaO)₃(BO₃)₄ (0.05 ≤ y ≤ 0.6) and Y_0.95-zBi_0.05Tb_zCa₃(GaO)₃(BO₃)₄ (0.05 ≤ z ≤ 0.6), and color-tunable emissions from blue to red, or from blue to green were realized in these two series of phosphors.

Crystal Structure, Vibrational, Spectroscopic and Thermochemical Properties of Double Sulfate Crystalline Hydrate [CsEu(H2O)3(SO4)2]·H2O and Its Thermal Dehydration Product CsEu(SO4)2

Crystalline hydrate of double cesium europium sulfate [CsEu(H2O)3(SO4)2]·H2O was synthesized by the crystallization from an aqueous solution containing equimolar amounts of 1Cs+:1Eu3+:2SO42− ions. Anhydrous salt CsEu(SO4)2 was formed as a result of the thermal dehydration of the crystallohydrate. The unusual effects observed during the thermal dehydration were attributed to the specific coordination of water molecules in the [CsEu(H2O)3(SO4)2]·H2O structure. The crystal structure of [CsEu(H2O)3(SO4)2]·H2O was determined by a single crystal X-ray diffraction analysis, and the crystal structure of CsEu(SO4)2 was obtained by the Rietveld method. [CsEu(H2O)3(SO4)2]·H2O crystallizes in the monoclinic system, space group P21/c (a = 6.5574(1) Å, b = 19.0733(3) Å, c = 8.8364(2) Å, β = 93.931(1)°, V = 1102.58(3) Å3). The anhydrous sulfate CsEu(SO4)2 formed as a result of the thermal destruction crystallizes in the monoclinic system, space group C2/c (a = 14.327(1) Å, b = 5.3838(4) Å, c = 9.5104(6) Å, β = 101.979(3) °, V = 717.58(9) Å3). The vibration properties of the compounds are fully consistent with the structural models and are mainly determined by the deformation of non-rigid structural elements, such as H2O and SO42−. As shown by the diffused reflection spectra measurements and DFT calculations, the structural transformation from [CsEu(H2O)3(SO4)2]·H2O to CsEu(SO4)2 induced a significant band gap reduction. A noticeable difference of the luminescence spectra between cesium europium sulfate and cesium europium sulfate hydrate is detected and explained by the variation of the extent of local symmetry violation at the crystallographic sites occupied by Eu3+ ions, namely, by the increase in inversion asymmetry in [CsEu(H2O)3(SO4)2]·H2O and the increase in mirror asymmetry in CsEu(SO4)2. The chemical shift of the 5D0 energy level in cesium europium sulfate hydrate, with respect to cesium europium sulfate, is associated with the presence of H2O molecules in the vicinity of Eu3+ ion.

Electrochemical Eu(iii) behaviours and Eu oxysulfate recovery over terpyridine-functionalized indium tin oxide electrodes

The Eu element was recovered as EuSO₄ over new terpyridine-functionalized ITO by an electrochemical method and luminescent Eu₂O₂SO₄ was obtained by post-thermal annealing.

Physico-chemical study of new supramolecular-architectured hybrid organic–inorganic sulfates incorporating diammoniumdiphenylsulfone cations

Two new hybrid organic–inorganic compounds, which incorporate 3,3′-diammoniumdiphenylsulfone or 4,4′-diammoniumdiphenylsulfone cations and sulfate anions, were synthesized and analyzed in detail.

Synthesis of Samarium OxysulfateSm2O2SO4 in the High-Temperature Oxidation Reaction and Its Structural, Thermal and Luminescent Properties

The oxidation process of samariumoxysulfide was studied in the temperature range of 500–1000 °C. Our DTA investigation allowed for establishing the main thermodynamic (∆Hº_exp = −654.6 kJ/mol) and kinetic characteristics of the process (E_a = 244 kJ/mol, A = 2 × 10¹⁰). The enthalpy value of samarium oxysulfate (ΔHºf (Sm₂O₂SO_4(monocl)) = −2294.0 kJ/mol) formation was calculated. The calculated process enthalpy value coincides with the value determined in the experiment. It was established that samarium oxysulfate crystallizes in the monoclinic symmetry class and its crystal structure belongs to space group C2/c with unit cell parameters a = 13.7442 (2), b = 4.20178 (4) and c = 8.16711 (8)Å, β = 107.224 (1)°, V = 450.498 (9)ų, Z = 4. The main elements of the crystalline structure are obtained and the cation coordination environment is analyzed in detail. Vibrational spectroscopy methods confirmed the structural model adequacy. The Sm₂O₂SO₄luminescence spectra exhibit three main bands easily assignable to the transitions from ⁴G_5/2 state to ⁶H_5/2, ⁶H_7/2, and ⁶H_9/2 multiplets.

Structural, Electronic and Vibrational Properties of YAl3(BO3)4

The crystal structure of YAl₃(BO₃)₄ is obtained by Rietveld refinement analysis in the present study. The dynamical properties are studied both theoretically and experimentally. The experimental Raman and Infrared spectra are interpreted using the results of ab initio calculations within density functional theory. The phonon band gap in the Infrared spectrum is observed in both trigonal and hypothetical monoclinic structures of YAl₃(BO₃)₄. The electronic band structure is studied theoretically, and the value of the band gap is obtained. It was found that the YAl₃(BO₃)₄ is an indirect band gap dielectric material.

K3Eu5(PO4)6: hydrothermal synthesis, crystal structure and photoluminescence properties

An anhydrous orthophosphate, K₃Eu₅(PO₄)₆ (tripotassium pentaeuropium hexaphosphate), has been prepared by a high-temperature solid-state reaction combined with hydrothermal synthesis, and its crystal structure was determined by single-crystal X-ray diffraction analysis (SC-XRD). The results show that the compound crystallizes in the monoclinic space group C2/c and the structure features a three-dimensional framework of [Eu₅(PO₄)₆]_∞, with the tunnel filled by K⁺ ions. The IR spectrum, UV-Vis spectrum and luminescence properties of polycrystalline samples of K₃Eu₅(PO₄)₆, annealed at temperatures of 650, 700, 750, 800 and 850 °C, were investigated. Although with a full Eu³⁺ concentration (9.96 × 10²¹ ions cm^-3), the self-activated phosphor K₃Eu₅(PO₄)₆ shows s strong luminescence emission intensity with a quantum yield of 37%. Under near-UV light excitation (393 nm), the series of samples shows the characteristic emissions of Eu³⁺ ions in the visible region from 575 to 715 nm. The sample sintered at 800 °C gives the strongest emission and its lifetime sintered at 800 °C (1.88 ms) is also the longest of all.