Ag-catalyzed synthesis of europium borate Eu(BO2)3 nanowires, growth mechanism and luminescent properties

Eu(BO₂)₃ nanowires with diameters of 10-20 nm were fabricated through direct sintering Eu(NO₃)₃·6H₂O and H₃BO₃ with Ag as catalyst. The result of X-ray diffraction (XRD) indicated that the nanowire was single-crystalline with body-centered monoclinic structure. Based on the fact that Ag nanoparticles attached to the tips and middles of nanowires, a vapor-liquid-solid (VLS) growth mechanism of the Eu(BO₂)₃ nanowires is proposed. Three well-defined stages have been clearly identified during the process: Ag-Eu-B-O cluster process, crystal nucleation, and axial growth. The photoluminescence characteristics under UV excitation were investigated. The dominated Eu³⁺ orange-red emission corresponding to the magnetic dipole transition ⁵D₀ → ⁷F₁ is centered at 591 nm, indicating that Eu³⁺ is located at high symmetry crystal field with inversion center.     

Preparation and luminescence properties of nanocrystalline La2O3:Eu phosphor

Powders La₂O₃ doped with 1 mol% Eu were prepared via a combustion route using different reducers (urea, glycine and citric acid). The structure and morphology were determined with XRD and HRTEM measurement. The main emission positions centered at 626 nm for ⁵D₀ → ⁷F₂ transition are observed. The variation of CT band with different reducers is observed. The intensity of ⁵D₀ → ⁷F₂ transition centered at 626 nm with respect to that of ⁵D₀ → ⁷F₁ transition is a function of the energy difference ΔE between the two CT band positions.     

The structure and spectroscopy of lanthanide(III) complexes with picolinic acid N-oxide in solution and in the solid state

The spectroscopic characteristics and the crystal structure of Eu(III) complex with picolinic acid N-oxide ligand, picNO, at room and liquid-nitrogen temperatures are discussed. Studies concerning the Eu(III) ion luminescence (intensity, luminescence lifetime measurements, and excitation spectra of the ⁵D₀ → ⁷F₀ transition) are presented. The selective excitation luminescence spectroscopy of Eu(III) in the range of the ⁵D₀ → ⁷F₀ transition is used for the study of Eu/picNO complexes in solution equilibria. In the crystal the complex molecules build the two-dimensional structures with additional Na⁺ cations and water molecules. This structure consists of edge-sharing chains of Na distorted octahedral, interconnected by Eu polyhedra (distorted square antiprisms). The ligand, pyridine-2-carboxylate-1-oxide, coordinates to the Eu(III) ion as an ionic bidentate chelate, forming the Na[Eu(picNO)₄] complex of six-membered chelate rings with the bite angles of ca. 70.5°. The complex is symmetrical; the Eu(III) ion is eight-coordinated.     

A red-emitting phosphor of fully concentrated Eu-based molybdenum borate Eu2MoB2O9

The fully concentrated Eu³⁺-based molybdenum borate Eu₂MoB₂O₉ was synthesized by the solid-state reaction method. The photoluminescence excitation and emission spectra, the temperature dependent luminescence intensities and the decay curve were investigated. Photoluminescence spectra show that the phosphor can be efficiently excited by near-UV light and exhibits an intense red luminescence corresponding to the electric dipole transition ⁵D₀ → ⁷F₂ at 615 nm. The luminescence intensities and color purity were investigated by increasing the fired temperatures. The phosphor shows the stable luminescence and color purity at high temperature.     

Synthesis of high efficient nanosized Y(V,P)O4:Eu red phosphors by a new technique

A new synthesis technique (liquid-phase precursor method) has been employed to synthesize nanosized Y(V,P)O₄:Eu³⁺ red phosphor particles of size 10-35 nm. X-ray diffraction analysis confirmed the synthesis of single phase Y(V,P)O₄:Eu³⁺ nanoparticles with tetragonal structure. The surface treatment with the KOH ionic solution at room temperature enhanced the grain growth (40-70 nm) of the nanoparticles. The possible grain growth mechanism is explained on the basis of formation of more OH⁻ groups in the solid solution after KOH introduction. The photoluminescence spectra obtained from the nanophosphors showed strong red luminescence due to ⁵D₀ → ⁷F_2,4 forced electric dipole transition. The luminescence intensity of the KOH-treated nanophosphors is comparable (about 70%) with the commercial sample.     

Photoluminescence properties of NaGd(MoO4)2:Eu nanophosphors prepared by sol-gel method

NaGd(MoO₄)₂:Eu³⁺ (hereafter NGM:Eu) phosphors have been prepared by sol-gel method. The properties of the resulting phosphors are characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), photoluminescence (PL) spectra and decay curve. The excitation spectra of NGM:Eu phosphors are mainly attributed to O → Mo charge-transfer (CT) band at about 282 nm and some sharp lines of Eu³⁺ f-f transitions in near-UV and visible regions with two strong peaks at 395 and 465 nm, respectively. Under the 395 and 465 nm excitation, intense red emission peaked at 616 nm corresponding to ⁵D₀ → ⁷F₂ transition of Eu³⁺ are observed for 35 at.% NGM:Eu phosphors as the optimal doping concentration. The luminescence properties suggest that NGM:Eu phosphor may be regarded as a potential red phosphor candidate for near-UV and blue light-emitting diodes (LEDs).     

The role of the annealing temperature on the optical and structural properties of Eu doped GaN/AlN QD

Self assembled molecular beam epitaxy grown GaN quantum dots stacked with AlN spacers were implanted with Eu ions. The as-implanted samples were further submitted to thermal annealing treatments in nitrogen, between 1000 °C and 1200 °C. Eu³⁺ luminescence was observed in all samples with the most intense emission assigned to the ⁵D₀ → ⁷F₂ transition in the red spectral region. The preferential excitation paths of Eu³⁺ luminescence is explored using photoluminescence excitation measurements which allow us to identify the feeding mechanisms for the Eu³⁺ ions inside the GaN quantum dots and AlN host. Optically active Eu centres in both GaN QD and AlN layers could be identified. For low implantation fluence the Eu centres inside GaN QD are dominant while for high fluences the emission arises from Eu in the AlN layers. The annealing temperature, on the other hand, does not cause any change in the local environment of the Eu-ions.     

A novel fluorinated europium ternary complex for highly efficient pure red electroluminescence

A novel fluorine-functionalized europium(III) ternary complex, i.e., Eu(DBM)₃(BFPP), in which DBM was dibenzoylmethane and BFPP 2, 3-bis(4-fluorophenyl)pyrazino[2,3-f] [1,10]phenanthroline, was designed, synthesized and characterized. The complex emits the characteristic red emission of trivalent europium ion due to the ⁵D₀ → ⁷F_j (j = 0–4) transitions under photo excitation with good luminescent quantum efficiency (0.55) and exhibits high thermal stability (387 °C). The organic light-emitting diodes (OLEDs) employing the complex as a dopant emitter with the structures of ITO/TPD (40 nm)/CBP:Eu-complex (30 nm)/Bphen (10 nm)/Alq₃ (20 nm)/LiF (1 nm)/Al (150 nm) were successfully fabricated. The 4 wt.% Eu(DBM)₃(BFPP) doped device exhibited the maximum luminance of 1766 cd/m² and a peak current efficiency of 4.6 cd/A, corresponding to the high external quantum efficiency of 2.27%.     

New complexes of europium and gadolinium with 2,4,6-trichlorophenyl acetoacetate as ligand

The synthesis, characterization and photoluminescent properties of new europium complexes with 2,4,6-trichlorophenyl acetoacetate (TCA) and 3-amino-2-carboxypyridine-N-oxide (picNO) ligands have been investigated. Results of the characterization are in agreement with the molecular formula proposed. The emission spectra at 77 K of the [Eu(TCA)₂(H₂O)₅]OH and [Eu(TCA)₂(picNO)(H₂O)₂]OH complexes, excited at 333 nm, display the typical transitions of the europium ion, ⁵D₀ → ⁷F_J (J = 0-4), indicating an efficient luminescence sensitization of this ion by the TCA ligand. The satisfactory agreement between experimental and theoretical absorption spectra of the organic part of the complexes suggests that the geometries optimized by the Sparkle model are correct. These results suggest these complexes as potential candidates as useful markers.     

Polymer composite P3HT:Eu doped La2O3 nanoparticles as a down-converter material to improve the solar spectrum energy

Europium-doped La₂O₃ nanocrystalline powders with sizes in the range of 50-200 nm have been obtained by the modified sol-gel Pechini method. These nanocrystals have been deagglomerated using sonication for 3 h and have been dispersed into a semiconductor P3HT polymeric matrix. We studied and analysed the spectroscopic properties of the trivalent europium in the hexagonal La₂O₃ nanocrystals dispersed in the polymer. The luminescence spectrum of Eu³⁺ in these nanocrystals is dominated by the ⁵D₀ → ⁷F₂ transition with a maximum intensity peak located at 626 nm. We observed that P3HT absorbs part of the light emitted by the nanoparticles. These properties look promising for using this material as a down-converter material in solar cells.     

Eu doped silica xerogel luminescent layer having antireflection and spectrum modifying properties suitable for solar cell applications

A spectrum modifying glassy luminescent layer with antireflection properties has been prepared with Eu³⁺ ions embedded in silica gel for solar cell applications. Preparation of such matrix by sol-gel process and change in luminescence properties in transforming from amorphous to crystalline phase are described. Luminescent Eu³⁺ species in amorphous silica matrix show intense red emission at 614 nm by absorbing UV/blue light. Amorphous environment with reduced symmetry for Eu³⁺ ions results in an unprecedented short decay time of 145 μs for ⁵D₀-⁷F₂ electric dipole transition. In the crystalline monoclinic phase of Eu₂O₃ nanoparticles, concentration quenching of Eu³⁺ species reduces luminescence output.     

Electroluminescence of a device based on europium β-diketonate with phosphine oxide complex

Rare earth (RE) ions have spectroscopic characteristics to emit light in narrow lines, which makes RE complexes with organic ligands candidates for full color OLED (Organic Light Emitting Diode) applications. In particular, β-diketone rare earth (RE³⁺) complexes show high fluorescence emission efficiency due to the high absorption coefficient of the β-diketone and energy transfer to the central ion. In this work, the fabrication and the electroluminescent properties of devices containing a double and triple-layer OLED using a new β-diketone complex, [Eu(bmdm)₃(tppo)₂], as transporting and emitting layers are compared and discussed. The double and triple-layer devices based on this complex present the following configurations respectively: device 1: ITO/TPD (40 nm)/[Eu(bmdm)₃(tppo)₂] (40 nm)/Al (150 nm); device 2: ITO/TPD (40 nm)/[Eu(bmdm)₃(tppo)₂] (40 nm)/Alq₃ (20 nm)/Al (150 nm) and device 3: ITO/TPD (40 nm)/bmdm-ligand (40 nm)/Al (150 nm), were TPD is (N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1-biphenil-4,4-diamine) and bmdm is butyl methoxy-dibenzoyl-methane. All the films were deposited by thermal evaporation carried out in a high vacuum system. These devices exhibit high intensity photo- (PL) and electro-luminescent (EL) emission. Electroluminescence spectra show emission from Eu³⁺ ions attributed to the ⁵D₀ to ⁷F_J (J = 0, 1, 2, 3 and 4) transitions with the hypersensitive ⁵D₀ → ⁷F₂ transition (around 612 nm) as the most prominent one. Moreover, a transition from ⁵D₁ to ⁷F₁ is also observed around 538 nm. The OLED light emission was almost linear with the current density. The EL CIE chromaticity coordinates (X = 0.66 and Y = 0.33) show the dominant wavelength, λ_d = 609 nm, and the color gamut achieved by this device is 0.99 in the CIE color space.     

Preparation and optical properties of silica gels doped with a new Eu(III) complex

The preparation and incorporation in silica gels of a novel europium complex, [Eu(ntac)₃][pphendcn] containing 4,4,4-trifluoro-1-(naphthalene-2-yl) butan-1,3-dione (Hntac) and pyrazino[2,3-f][1,10-phenathroline-2,3-dicarbonitrile (pphendcn) is demonstrated. An effective energy transfer from the organic ligands to the Eu(III) ions leads to a strong f-f luminescence even at low activator concentrations, n_Eu/n_Si ≈ 1 × 10⁻⁵. The new amorphous materials are characterized by UV/Vis reflectance and transmission spectroscopy, luminescence/excitation spectroscopy, X-ray diffraction, elemental analysis, IR spectroscopy, DTA/TG and NMR. The optical properties of gels with a different Eu(III) doping are discussed. The stability of the europium complex in the silica matrix during time (up to 4 months) and after heating is discussed. The Eu(III) spectra-structure correlation is used to characterize the site symmetry of the activator.     

Luminescent micro- and nanofibers based on novel europium phthalate complex

We synthesized by wet chemical route a novel europium–potassium phthalate complex Eu³⁺K⁺[(COO)₂(C₆H₄)]₂. The compound is a white powder insoluble in water. X-ray diffraction evaluation shows that we obtained a new crystalline compound with no traces of the starting materials (potassium hydrogen phthalate and europium chloride). Scanning electron microscopy reveals that the powder consists of fiber-shaped structures with sizes larger than 250 nm in diameter. Energy dispersive X-ray analysis proves that the compound has a 1:1 europium–potassium ratio. Fourier transform infrared spectroscopy confirms the presence of the phthalate in the new compound. Photoluminescence and cathodoluminescence measurements show that the fiber-shaped structures are intensely luminescent with emission bands corresponding to the ⁵D₀ → ⁷F_J (J = 1–4) Eu (III) ion’s transitions in the region between 580 nm and 700 nm, the most intense maximum being observed around 615 nm. Up-converted luminescence with a maximum at 315 nm was recorded.     

The effect of Eu-activated InVO4 phosphors prepared by sol-gel method

Indium orthovanadate (InVO₄) doped with Eu³⁺ ions had been synthesized by sol-gel method. The precursor of InVO₄:Eu³⁺ powders were heated at 950 °C for 6 h in air, and the crystal structure, surface morphologies and photoluminescence properties were also investigated. XRD patterns indicated that the crystallinity of InVO₄:Eu³⁺ powders decreases with increasing Eu³⁺ ion concentrations. From the SEM micrographs, the shapes of the InVO₄ particles are uniform and like pebbles. With increasing Eu³⁺ ion concentrations, the shapes of the InVO₄:Eu³⁺ particles become smaller and irregular. In the PL studies, the sharp excitation peaks between 300 and 600 nm correspond to the Eu³⁺ intra-4f transitions. Excitation at 326 nm in terms of Eu³⁺ concentrations in (In_1−xEu_x)VO₄ powders shows that the (In_1−xEu_x)VO₄ phosphors display bright red luminescence at about 615 nm belonging to the ⁵D₀ → ⁷F₂ electric dipole transition, and the time-resolved ⁵D₀ → ⁷F₂ transition presents a single exponential decay behavior. The concentration quenching is active when the Eu³⁺ concentration is larger than 30 mol%, and the critical distance is about 8.024 Å.     

Hydrothermal synthesis of GdBO3:Eu nanofibres

Large-scale GdBO₃:Eu³⁺ nanofibres with uniform diameter were controllably synthesized by a glycine-assisted hydrothermal method at 170 °C using Gd(NO₃)₃, Eu(NO₃)₃ and Na₂B₄O₇·10H₂O as the precursors. X-ray diffraction (XRD) results show that the luminescent nanofibres are pure hexagonal structure and no other impurity phase appeared. Transmission electron microscopy (TEM) studies indicate that GdBO₃:Eu³⁺ has a nanofibre structure. Photoluminescence (PL) spectra results demonstrate that the GdBO₃:Eu³⁺ nanofibres have three strong ⁵D₀ → ⁷F₁ (595 nm) and ⁵D₀ → ⁷F₂ (613 and 627 nm) transition peaks corresponding to orange-red and red colors, respectively.     

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.     

Photoluminescence and preparation of ZnNb2O6 doped with Eu and Tm nanocrystals for solar cell

Synthesis and luminescence properties of Eu³⁺ and Tm³⁺-doped ZnNb₂O₆ nanocrystals by the sol–gel process were investigated. The products were characterized by differential thermal analysis (DTA), scanning electron microscopy (SEM), and photoluminescence spectroscopy (PL). ZnNb₂O₆:Eu³⁺ shows bright red luminescence with maximum peak at 613 nm attributed to ⁵D₀ → ⁷F₂ transition. The major blue emission peak of ZnNb₂O₆:Tm³⁺ was at 483 nm, corresponding to the transitions ¹G₄ → ³H₆. The optimum concentration of Eu³⁺ and Tm³⁺ showing the maximum PL intensity was 4 mol% and 1 mol%, respectively.     

Luminescent and thermal properties of a novel red-emitting silicon fluoride acrylate-Eu(III) copolymer for white LEDs

A red-emitting silicon fluoride acrylate (SFA)-Eu(III) copolymer was prepared based on water-in-oil emulsion polymerization method. Its photoluminescence including the temporal decay was studied in addition to the thermal properties. Of the emissions due to the ⁵D₀ → ⁷F_J (J = 0–4) transitions of Eu³⁺ ions, an intense red emission due to ⁵D₀ → ⁷F₂ transition was observed at 618 nm under the 395 nm excitation, together with a weak ⁵D₀ → ⁷F₀ emission at 580 nm. Compared with some commercial phosphor, the SFA-Eu(III) copolymer also have a higher QE value. From the optical properties it was suggested that Eu³⁺ ions were located at the disordered non-inversion Eu³⁺ sites in the copolymer. The glass transition temperature (T_g) was estimated about −51.5 °C from a differential scanning calorimetric curve, while chemical decomposition was estimated to start from 385 °C from a thermogravimetry analysis curve. Taking into account the thermal stability in a wide temperature range from −51.5 °C to 385 °C, the SFA-Eu(III) copolymer is expected to act as a potential red component for near-UV excited white LEDs.     

Enhanced green emission from Tb-Bi co-doped GdAlO3 nanophosphors

Bi³⁺ and Tb³⁺ ions co-doped GdAlO₃ (GAP) nanophosphors have been synthesized by means of solvothermal reaction method. The XRD pattern of GAP phosphor confirms their orthorhombic phase. The luminescence properties of these phosphors have been explored by analyzing their excitation and emission spectra along with their decay curves. The excitation spectra of GAP:Tb³⁺, Bi³⁺ phosphors consist of a broad band in the shorter wavelength region due to the 4f⁸ → 4f⁷5d¹ transition of Tb³⁺ ions overlapped with the 6s² → 6s¹6p¹ (¹S₀ → ³P₁) transition of Bi³⁺ ions and some sharp peaks in the longer wavelength region due to f → f transitions of Tb³⁺ ions. The present phosphors exhibit green color due to strong ⁵D₄ → ⁷F₅ transition of Tb³⁺ ions. The emission intensity was enhanced by co-doping with Bi³⁺ ions under 292 nm excitation, which indicate that the efficient energy transfer occurred from Bi³⁺ to Tb³⁺ ions.