A new yellowish green luminescent material SrMoO4:Tb

A novel yellowish green phosphor tervalent terbium (Tb³⁺) doped strontium molybdate (SrMoO₄) was synthesized by conventional solid-state reaction method and its crystal structure and luminescent properties are investigated in this paper. The X-ray diffraction patterns (XRD) showed that the phosphor sintered at 750 °C for 3 h was a pure SrMoO₄ phase. The excitation spectrum consisted of two bands and the two excitation peaks located at 375 nm and 488 nm respectively. The emission spectrum was composed of four narrow bands, in which the strongest emission was located at 548 nm. The particle size analysis indicated that the median particle size D₅₀ = 2.89 μm and range of particle size distribution was narrow. These results showed that the SrMoO₄:Tb³⁺ phosphor was a promising yellowish green phosphor for ultraviolet light emitting diode (UVLED) and blue LED based white LED. The appropriate concentration of Tb³⁺ was 5 mol% for the highest emission intensity at 548 nm. Natrium ion (Na⁺) was found to be a promising charge compensator for SrMoO₄:Tb³⁺ phosphor.     

Hydrothermal formation and characteristics of rare-earth niobate phosphors and solid solutions between YNbO4 and TbNbO4

Monoclinic fergusonite-type niobate, YNbO₄:Tb³⁺ and complete solid solutions with luminescent properties in the YNbO₄–TbNbO₄ system were directly formed as nanocrystals from the precursor solutions of NbCl₅, TbCl₃, and YCl₃ under hydrothermal conditions at 240 °C. The niobate nanocrystals possessed distinguishing feature of ellipsoidal morphology. The optical band gap of the as-prepared samples, Y_1−xTb_xNbO₄, x = 0–1.0, decreased from 3.7 to 2.9 eV as the terbium concentration increased from x = 0 to 1.0. The photoluminescence spectra of the as-prepared nanocrystals containing terbium are responsible for the characteristic blue (490 nm) and green (545 nm) luminescence, associated with ⁵D₄ → ⁷F₆ and ⁵D₄ → ⁷F₅ transitions, respectively. The strongest emission bands in the green spectral domain corresponding to ⁵D₄ → ⁷F₅ transition of Tb³⁺ are located at 545 and 550 nm under excitation at 240 nm Xe lamp. By heat treatment at 1300 °C, the luminescence intensity of the as-prepared solid solution x = 0.10 that presented the highest photoluminescence intensity increased more than 8 times as high as that before heat treatment.     

Preparation and studies of Eu and Tb co-doped Gd2O3 and Y2O3 sol-gel scintillating films

Eu³⁺ (2.5 at.%) and Tb³⁺ (0.005-0.01 at.%) co-doped gadolinium and yttrium oxide (Gd₂O₃ and Y₂O₃) powders and films have been prepared using the sol-gel process. High density and optical quality thin films were prepared with the dip-coating technique. Gadolinium (III) 2,4-pentadionate and yttrium (III) 2,4-pentadionate were used as precursors, and europium and terbium in their nitrate forms were used as doping agents. Chemical and structural analyses (infrared spectroscopy, X-ray diffraction and high-resolution transmission electron microscopy) were conducted on both sol-gel precursor powders and dip-coated films. The morphology of thin films heat-treated at 700 °C was studied by means of atomic force microscopy. It was shown that the highly dense and very smooth films had a root mean roughness (RMS) of 2 nm ± 0.2 (A = 0.0075 Tb³⁺) and 24 nm ± 3.0 (B = 0.01 Tb³⁺). After treatment at 700 °C, the crystallized films were in the cubic phase and presented a polycrystalline structure made up of randomly oriented crystallites with grain sizes varying from 20 to 60 nm. The X-ray induced emission spectra of Eu³⁺- and Tb³⁺-doped Gd₂O₃ and Y₂O₃ powders showed that Tb³⁺ contents of 0.005, 0.0075 and 0.01 at.% affected their optical properties. Lower Tb³⁺ concentrations (down to 0.005 at.%) in both systems enhanced the light yield.     

Synthesis of Tb3Al5O12 (TAG) transparent ceramics for potential magneto-optical applications

Tb₃Al₅O₁₂ transparent ceramics have been prepared by solid state reaction and vacuum sintering. The optical quality and the microstructure of the samples were investigated. The sample sintered at 1650 °C possessed relatively good optical transparency from 400 nm to 1600 nm. The Verdet constant measured at 632.8 nm of the quasi-pore-free Tb₃Al₅O₁₂ transparent ceramic was −172.72 rad T⁻¹ m⁻¹, which was close to the counterpart of Tb₃Al₅O₁₂ single crystal. The thermal conductivity of the sample was also measured. To the best of our knowledge, this is the first time that Tb₃Al₅O₁₂ transparent ceramic with relatively good optical quality and magneto-optical property has been reported.     

Purification and crystal growth of LiY0.5Er0.5F4 crystals

The purification procedure of the LiY_0.5Er_0.5F₄ compound for Bridgman-Stockbarger and Czochralski single crystal growth has been investigated. Yttrium and rare-earth oxyfluorides were found to form during hydrofluoric heat-treatment of the starting fluoride mixture. Optically clear single crystals of purified LiY_0.5Er_0.5F₄ were grown by both Bridgman-Stockbarger and Czochralski methods. The stoichiometry was investigated by magnetic susceptibility measurements and the Er content in the single crystals grown by both Bridgman-Stockbarger and Czochralski methods were found to fit stoichiometry within the measurement error. No free (OH)^? ions were found by infrared absorption spectroscopy.     

Electronic structure and photoluminescence properties of Eu-activated Ca4Si2O7F2

The blue-emitting phosphors Ca_(4−x)Eu_xSi₂O₇F₂ (0 < x ? 0.05) have been prepared by solid-state reaction and the photoluminescence properties have been studied systematically. The electronic structure of calcium fluoride silicate Ca₄Si₂O₇F₂ was calculated using the CASTEP code. The calculation results of electronic structure show that Ca₄Si₂O₇F₂ has an indirect band gap with 5 eV. The top of the valence band is dominated by O 2p and Si 3p states, while the bottom of the conduction band is mainly composed of Ca 3d states. Under the 350 nm excitation, the obtained sample shows a broad emission band in the wavelength range of 400-500 nm with peaks of 413 nm and 460 nm from two different luminescence centers, respectively. The relative intensity of the two peaks changes with the alteration of the Eu²⁺ concentration. The strong excitation bands of the powder in the wavelength range of 200-420 nm are favorable properties for the application as lighting-emitting-diode conversion phosphor.     

Hochdrucksynthesen und transformationen von alkali-oxofluoro-metallaten des typs Cs2NaMOxF6−x und Rb2LiMOxF6−x

Compounds and mixtures of compositions Cs₂NaMO_xF_6?x and Rb₂LiMOF₅ were transformed under high pressure to metastable modifications crystallizing in the hexagonal HT-K₂LiAlF₆ type structure and/or the cubic K₂NaCrF₆ elpasolithe type structure.Mixtures of composition Rb₂LiMO_xF_6?x (M = Nb⁵⁺or Mo⁶⁺) yielded under high pressure besides LiF metastable compounds A₂MO_xF_5?x crystallizing orthorhombic in the K₂VO₂F₃ type structure.     

Luminescence excitation spectra of TbX3 (X = Cl, Br, I)

A systematic study of the excitation spectrum of TbX₃ (X = Cl⁻, Br⁻, I⁻) is presented in this work. In general, the excitation spectra of TbX₃ can be divided into three major regions: (1) the short-wave host lattice absorption region, (2) the intermediate absorption region where the Tb³⁺ 4f⁸ → 4f⁷5d¹ interconfigurational excitation transition are located, and (3) the long-wave excitation region where the Tb³⁺ 4f⁸ → 4f⁸ intraconfigurational excitation transition are located. The high spin and the low spin components of the Tb³⁺ interconfigurational excitation transition are clearly identified in the case of TbCl₃. The luminescence of TbX₃ (X = Cl⁻, Br⁻, I⁻) is dominated by emission transitions emanating from the Tb³⁺⁵D₄ state. A comparative study of the optical properties of TbX₃ (X = Cl⁻, Br⁻, I⁻) with the properties of the Tb³⁺ ion in several halide host lattices is presented. Further, a comparative study of the fundamental host lattice optical transitions in terbium halides and other halide materials is also presented.     

Crystal structure of K5NdLi2F10

A single-crystal x-ray diffraction analysis has been performed on K₅NdLi₂F₁₀ synthesized from a melt containing an excess of KF and LiF as a flux. The structure is orthorhombic with space group Pnma, Z = 4, and cell parameters a = 20.65, b = 7.779, $\text{c}\text{= 6.902}\text{A}\text{?}$. A full-matrix least squares refinement gave R = 0.08 for 1056 independent reflections. The basic structural features are sheets, perpendicular to the a-axis, formed by isolated NdF₈ dodecahedra and LiF₄ tetrahedra. The sheets are held together by the K⁺ ions. The compound K₅NdLi₂F₁₀ is the first reported fluoride in which the Nd polyhedra are isolated from each other. The shortest Nd-Nd distance is 6.72 Å, and the concentration of Nd³⁺ ions is 3.60 × 10²¹ cm^?3.     

M2Y8(SiO4)6O2: Tb (M = Ca, Sr) phosphors: Sol-gel synthesis from N-2-aminoethylic-3-aminopropyldiethoxysilane and different photoluminescence behavior

M₂Y₈(SiO₄)₆O₂: Tb³⁺ (M = Ca, Sr) phosphors have been synthesized with a new silicon source silane crosslinking reagent (N-2-aminoethylic-3-aminopropyldiethoxysilane [NH₂(CH₂)₂NH(CH₂)₃SiCH₃(OCH₃)₂], abbreviated as AEAPMMS) through the sol-gel process, both of which present the characteristic emission ⁵D₄ → ⁷F_J (J = 6, 5, 4, 3) of Tb³⁺ ions. It is interesting to be found that the high energy level blue emission (⁵D₃ → ⁷F_J (J = 6, 5, 4, 3) transition) still can be found in the emission spectrum of Ca₂Y₈(SiO₄)₆O₂: Tb³⁺ while it disappears in the emission spectrum of Sr₂Y₈(SiO₄)₆O₂: Tb³⁺ for the cross-relaxation-induced quenching.     

Rapid synthesis of single-crystalline TbF3 with novel nanostructure via ultrasound irradiation

Terbium fluoride (TbF₃) nanopeanut has been successfully synthesized via a mild sonochemical route from an aqueous solution of terbium nitrate and fluoroborate without any template or organic additive. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and photoluminescence (PL) spectra were utilized to characterize the synthesized samples. The morphologies and optical properties of the obtained TbF₃ nanopeanut can be tuned by ultrasound irradiation as well as the fluoride source. The prepared TbF₃ nanopeanut shows extraordinarily high room temperature photoluminescence intensity comparing to the products prepared by stirring. The possible formation mechanism is proposed in this paper.     

Multifunctional γ-Fe2O3@Ca3(PO4)2@YPO4:Tb,Ce nanocomposites as a potential drug carrier

Multifunctional γ-Fe₂O₃@Ca₃(PO₄)₂@YPO₄:Tb³⁺,Ce³⁺ nanocomposites were synthesized using an easy direct-precipitation method. The nanocomposites had a monodispersed spherical morphology with a narrow size distribution, and dispersed well in water. The nanocomposites showed the characteristic emission peaks of Ce³⁺ (5d–4f) and Tb³⁺ (⁵D₄–⁷F₃ to ⁵D₄–⁷F₆). Magnetism measurements revealed that the samples were nearly superparamagnetic. The multifunctional nanocomposites were used for in vitro drug delivery tests under ambient conditions, and we discuss the influence of different media on the release of cisplatin (cis-diamminedichloroplatinum). We assessed the loading and release performance for cisplatin by means of UV–visible spectrophotometry. Our findings will provide guidance for engineering similar multifunctional nanocomposites for use in future drug delivery applications.     

Luminescent efficiency of Eu3+ and Tb3+ in LaMgB5O10 — Type borates under excitation from 100 to 400 nm

Luminescent properties of Eu³⁺ and Tb³⁺ in doped LaMgB₅O₁₀ have been studied over the 100–400 nm excitation range. The Tb³⁺-activated borate shows an external quantum efficiency exceeding 75 % when excited in 5d levels between 180 and 205 nm. The excitation range of high efficiency is extended up to 290 nm when the terbium fluorescence is sensitized by cerium, which makes this material a good candidate for use as the green component in low-pressure mercury lamps. The vacuum UV spectra of the Ln_xLa_1?xMgB₅O₁₀ (Ln = Eu, Tb) phases show a band close to 150 nm corresponding to an excitation of the Eu³⁺ and Tb³⁺ ions transmitted through the host lattice.     

Properties of Gd2O3:Eu, Tb nanopowders obtained by sol-gel process

A significant practical application for nanostructured materials is X-ray medical imagery, because it is necessary to use dense materials in order to enable absorption of high energy photons. An important requirement of these materials is UV-vis range emission produced by X-ray excitation, which can be influenced by the particle size. Europium doped gadolinium oxide is a well known red phosphor. Moreover, nanophosphors of Gd₂O₃ codoped with Tb³⁺, Eu³⁺ increase their light yield by energy transfer between Tb³⁺ and Eu³⁺. In this study, Gd₂O₃ nanopowders codoped with Eu³⁺ and Tb³⁺ (2.5 at.% Eu³⁺, and 0.005 and 0.01 at.% Tb³⁺) were obtained via a sol-gel process using gadolinium pentanedionate as precursor and europium and terbium nitrates as doping sources. In this paper, we report the influence of annealing temperature on the structure, morphology and luminescent properties of Gd₂O₃:Eu³⁺, Tb³⁺ by means of TGA, XRD, TEM and X-ray emission measurements.     

Near-ultraviolet excitable Ca4Y6(SiO4)6O: Ce,Tb white phosphors for light-emitting diodes

The present investigation aims to demonstrate the potentiality of Tb³⁺ and Ce³⁺ co-doped Ca₄Y₆(SiO₄)₆O phosphors. By incorporation of Ce³⁺ into Ca₄Y₆(SiO₄)₆O: Tb³⁺, the excitation band was extended from short-ultraviolet to near-ultraviolet region. The energy transfer from Ce³⁺ to Tb³⁺ in Ca₄Y₆(SiO₄)₆O host was investigated and demonstrated to be a resonant type via a dipole–dipole mechanism with the critical distance of 10.2 Å. When excited by 352 nm, Ca₄Y₆(SiO₄)₆O: Ce³⁺, Tb³⁺ exhibited a brighter and broader violet-blue emission (421 nm) from the Ce³⁺ and an intense green emission (542 nm) from the Tb³⁺. Combining the two emissions whose intensities were adjusted by changing the doping levels of the co-activator, an optimized white light with chromaticity coordinates of (0.278, 0.353) is generated in Ca₄Y₆(SiO₄)₆O: 2% Ce³⁺, 8% Tb³⁺, and this phosphor could be potentially used in near-ultraviolet light-emitting diodes.     

Observation on long afterglow of Tb in CaWO4

The Tb³⁺ doped CaWO₄ phosphors are synthesized via high temperature solid state reaction. The X-ray diffraction shows that small amount of Tb³⁺ does not have a significant influence on the structure of CaWO₄. A broad absorption band of the WO₄²⁻ group is observed from photoluminescence and the energy transfer from WO₄²⁻ group to Tb³⁺ ions induces the f-f transition. The cross-relaxation between two adjacent Tb³⁺ ions weakens ⁵D₃-⁷F_j transitions and enhances the ⁵D₄-⁷F_j transitions, leading to a green long afterglow of the phosphors. The thermoluminescence curves centered around 75 °C reveal the trap depth for afterglow generation is about 0.74-0.77 eV. The optimum Tb³⁺ concentration for afterglow properties is about 1%. A deep hole trap is induced when Tb³⁺ concentration exceeds 1% and it suppresses the thermoluminescence and the decay properties.     

Magnetic properties of new ternary silicides : Tb2Ir3Si5 and both polymorphic forms of TbIr2Si2

A new ternary silicide Tb₂Ir₃Si₅ of U₂Co₃Si₅-type structure has been prepared as well as two polymorphic forms of TbIr₂Si₂. Both modifications are tetragonal, the low-and high-temperature forms are isostructural with ThCr₂Si₂ and CaBe₂Ge₂ respectively. The three compounds order antiferromagnetically. A high Néel temperature is observed for the low-temperature modification (T_N = 80K, θ_p = 42K). Its magnetic structure is similar to that of TbRh₂Si₂ for which ferromagnetic layers perpendicualr to the c-axis are coupled antiferromagnetically (+?+?). Tb₂Ir₃Si₅ and the high-temperature modification of TbIr₂Si₂ have low T_N and θ_p values. The difference observed in the magnetic behavior of these compounds is likely due to the influence of the environment of the Tb³⁺ ion on the density of states at Fermi level.     

Hydrothermal synthesis and luminescent properties of Y2O3:Tb and Gd2O3:Tb microrods

One-dimensional (1D) Y₂O₃:Tb³⁺ and Gd₂O₃:Tb³⁺ microrods have been successfully prepared through a large-scale and facile hydrothermal method followed by a subsequent calcination process in N₂/H₂ mixed atmosphere. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (IR), thermogravimetric analysis (TGA), energy-dispersive X-ray spectra (EDX), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), photoluminescence (PL) and cathodoluminescence (CL) spectra as well as kinetic decays were used to characterize the samples. The as-formed products via the hydrothermal process could transform to cubic Y₂O₃:Tb³⁺ and Gd₂O₃:Tb³⁺ with the same morphology and slight shrinking in size after a postannealing process. Both Y₂O₃:Tb³⁺ and Gd₂O₃:Tb³⁺ microrods exhibit strong green emission corresponding to ⁵D₄ → ⁷F₅ transition (542 nm) of Tb³⁺ under UV light excitation (307 and 258 nm, respectively), and low-voltage electron beam excitation (1.5 → 3.5 kV), which have potential applications in fluorescent lamps and field emission displays.     

Distribution du fluor et de l'oxygene dans l'oxyfluorotantalate de potassium K2Ta4O9F4

The crystal structure of potassium tantalum oxide fluoride K₂Ta₄O₉F₄ has been previously determined by X ray-diffraction, but this technique is unable to distinguish in the lattice between oxygen and fluorine atoms. From NMR measurements on ¹⁹F it is possible by a Van Vleck second moment approach to locate the F^? ions at the corners of the octahedra, forming infinite Ta-F-Ta … chains along the $\text{c}$ axis.