Synthesis and luminescence properties of YVO4:Eu nanocrystals grown in nanoporous glass

We report on a feasible method to synthesize luminescence nanocrystals in porous glass in this paper. Well dispersed YVO₄:Eu nanocrystals were proved being grown in nanoporous glass by XRD, micro-Raman spectra and HRTEM equipped with EDS. The YVO₄:Eu³⁺ nanocrystal grown in porous glass herein shows very different luminescence properties compared with single Eu-doped sample. By this method, intense red emission from high silica glass due to energy transfers VO₄³⁻ → Eu³⁺ was obtained. The results show that the reduction from Eu³⁺ to Eu²⁺ in porous glass impregnated with Eu³⁺ ions was avoided effectively.     

Hydrothermal synthesis and optical properties of Eu doped NaREF4 (RE = Y, Gd), LnF3 (Ln = Y, La), and YF3·1.5NH3 micro/nanocrystals

5 mol% Eu³⁺ doped NaYF₄ (α-, β-), YF₃, YF₃·1.5NH₃, NaGdF₄, and LaF₃ micro/nanocrystals have been synthesized by a hydrothermal method. The final products are characterized by X-ray diffraction, field emission scanning electron microscopy, photoluminescence excitation and emission spectra, and luminescent dynamic decay curves. Due to its sensitivity to local symmetry, Eu³⁺ shows different optical properties in the above samples. It has stronger luminescent intensity in β-NaYF₄ than that in α-NaYF₄ while it exhibits different higher energy ⁵D_1,2 to lower ⁷F_J emissions as well as the asymmetric ratios and the splits of ⁵D₀ → ⁷F₁, ⁷F₄. YF₃, LaF₃, and β-NaGdF₄ have analogous optical intensities to those of β-NaYF₄. However, β-NaGdF₄ has the similar spectral profile to that of β-NaYF₄ while YF₃ and LaF₃ have the opposite cases in the ⁵D₀ → ⁷F₂, ⁷F₁ emissions. Further, Judd-Ofelt calculation has been used to analyze the experimental phenomena.     

Synthesis and optical properties of (Gd1−x,Eux)2O2SO4 nano-phosphors by a novel co-precipitation method

(Gd_1−x,Eu_x)₂O₂SO₄ nano-phosphors were synthesized by a novel co-precipitation method from commercially available Gd₂O₃, Eu₂O₃, H₂SO₄ and NaOH starting materials. Composition of the precursor is greatly influenced by the molar ratio of NaOH to (Gd_1−x,Eu_x)₂(SO₄)₃ (the m value), and the optimal m value was found to be 4. Fourier transform infrared spectrum (FT-IR) and thermal analysis show that the precursor (m = 4) can be transformed into pure (Gd_1−x,Eu_x)₂O₂SO₄ nano-phosphor by calcining at 900 °C for 2 h in air. Transmission electron microscope (TEM) observation shows that the Gd₂O₂SO₄ phosphor particles (m = 4) are quasi-spherical in shape and well dispersed, with a mean particle size of about 30-50 nm. Photoluminescence (PL) spectroscopy reveals that the strongest emission peak is located at 617 nm under 271 nm light excitation, which corresponds to the ⁵D₀ → ⁷F₂ transition of Eu³⁺ ions. The quenching concentration of Eu³⁺ ions is 10 mol% and the concentration quenching mechanism is exchange interaction among the Eu³⁺ ions. Decay study reveals that the ⁵D₀ → ⁷F₂ transition of Eu³⁺ ions has a single exponential decay behavior.     

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.     

Behaviour of the EuD0 → F0 transition in CaMoO4 powellite type ceramics under Ar and Pb ions implantation

In this work, the Eu³⁺⁵D₀ → ⁷F₀ transition is used as a structural probe to follow the Eu³⁺ environment modification in powellite CaMoO₄ under irradiation or when its composition is varying. Six ceramics with compositions ranging from Ca_0.99Eu_0.01MoO₄ to Ca_0.76Sr_0.1Na_0.07 Eu_0.01La_0.02Nd_0.02Pr_0.02 MoO₄ were synthesized and each composition has a specific Eu³⁺ luminescence signal. The ⁵D₀ → ⁷F₀ transition appeared to be a very sensitive structural probe. Even if there is only one structural site in powellite for europium, the Eu³⁺⁵D₀ level position changes with the modification of the Eu³⁺ cationic neighbours. Low ⁵D₀ values are observed for environments containing trivalent rare earth elements when high ⁵D₀ values are observed for Na⁺ rich environments. Under 8 MeV Ar ions irradiation, the Eu³⁺⁵D₀ → ⁷F₀ transition is not really affected. Under 108 MeV Pb ions irradiation there is an homogenization of the Eu³⁺⁵D₀ → ⁷F₀ transition from the different irradiated samples revealing a reorganization of the crystalline structure.     

Synthesis,characterization and photoluminescence properties of (Gd1−x,Eux)2O2SO4 sub-microphosphors by homogeneous precipitation method

(Gd_1−x,Eu_x)₂O₂SO₄ sub-microphosphors were synthesized by homogeneous precipitation method from commercially available Gd₂O₃, Eu₂O₃, H₂SO₄ and (NH₂)₂CO (urea) starting materials. Fourier transform infrared spectra show that the precursors with different molar ratios of (NH₂)₂CO to Gd₂(SO₄)₃ (the m value) are mostly composed of gadolinium hydroxyl, carbonate and sulfate groups with some crystal water. X-ray diffraction indicated that the precursor (m = 5) can be transformed into pure Gd₂O₂SO₄ phase after heat treated at 900 °C for 2 h in air. Field emission scanning electron microscope micrographs illustrate that the Gd₂O₂SO₄ phosphor particles (m = 5) are quasi-spherical in shape and well dispersed, with a mean particle size of about 300–500 nm. Photoluminescence spectroscopy reveals that the strongest emission peak for (Gd_1−x,Eu_x)₂O₂SO₄ sub-microphosphors is located at 618 nm under 270 nm light excitation, which corresponds to the ⁵D₀ → ⁷F₂ transition of Eu³⁺ ions. The quenching concentration of Eu³⁺ ions is 5 mol% and the concentration quenching mechanism is due to the electric dipole–dipole interaction. Decay study reveals that the ⁵D₀ → ⁷F₂ transition of Eu³⁺ ions fits with a mono exponential function.     

Substitution site and photoluminescence spectra of Eu-substituted SrTiO3 prepared by Pechini method

Eu³⁺-substituted SrTiO₃ (Sr_1 − xEu_xTiO₃) without second phase has been successfully prepared by Pechini method. X-ray diffraction patterns have suggested that solid-solubility limit would be 1-2 mol% due to large ionic radius difference between Eu³⁺ and Sr²⁺. Photoluminescence spectra of Sr_1 − xEu_xTiO₃ have shown the intense ⁵D₀-⁷F₁ transition higher than ⁵D₀-⁷F₂ transition, which indicates that Eu³⁺ was substituted for Sr²⁺ site.     

The transformation of Eu→Eu in SiO2-Al2O3-NaF-YF3: Eu glasses and glass ceramics

Transparent glasses and glass ceramics of SiO₂-Al₂O₃-NaF-YF₃: Eu³⁺ containing the YF₃ nano-crystals were prepared in air atmosphere and their spectroscopic properties are presented. The blue emission peaked at 433 nm shown in the spectra indicate the existence of Eu²⁺.The transformation of Eu³⁺→Eu²⁺ is related with the existence of F⁻, which is the key trigger for the transformation in air atmosphere. In addition, the emission intensities of Eu³⁺ and Eu²⁺ were also related with the concentrations of Eu³⁺. The emission intensities increased heavily with the increasing dopant of EuF₃ in both glasses and glass ceramics_. When the doped concentration of EuF₃ was higher than 0.5 mol.%, the concentration quenching effect occurred.     

Influence of excitation wavelengths on luminescent properties of Sr3Al2O6:Eu, Dy phosphors prepared by sol-gel-combustion processing

Eu²⁺ and Dy³⁺ ion co-doped Sr₃Al₂O₆ red-emitting long afterglow phosphor was synthesized by sol-gel-combustion methods using Sr(NO₃)₂, Al(NO₃)₃·9H₂O, Eu₂O₃, Dy₂O₃, H₃BO₃ and C₆H₈O₇·H₂O as raw materials. The crystalline structure of the phosphors were characterized by X-ray diffraction, luminescent properties of phosphors were analyzed by fluorescence spectrophotometer. The effect of excitation wavelengths on the luminescent properties of Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphors was discussed. The emission peak of Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphor lays at 516 nm under the excitation of 360 nm, and at 612 nm under the excitation of 468 nm. The results reveal that the Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphor will emit a yellow-green light upon UV illumination, and a bright red light upon visible light illumination. The emission mechanism was discussed according to the effect of nephelauxetic and crystal field on the 4f⁶5d¹ → 4f⁷ transition of the Eu²⁺ ions in Sr₃Al₂O₆. The afterglow time of (Sr_0.94Eu_0.03Dy_0.03)₃ Al₂O₆ phosphors lasts for over 600s after the excited source was cut off.     

A novel single-phased white light emitting phosphor of Eu ions-doped Ca2LaTaO6

A novel single-phased white light emitting phosphor, Ca₂(La_1−xEu_x)TaO₆ (x = 0.001–0.7), was synthesized using a vibrating milled solid state reaction. The results indicate that the emission spectra of Ca₂LaTaO₆:Eu³⁺ samples exhibit a series of shaped peaks assigned to the ⁵D₀ → ⁷F_J (J = 0, 1, 2, 3, 4) transitions under an excitation of 395 nm. The characteristic peaks of Eu³⁺ ion intra-4f transitions from excited states to lower levels include ⁵D₃ → ⁷F_J (J = 1, 2, 3), ⁵D₂ → ⁷F_J (J = 0, 1, 2, 3), ⁵D₁ → ⁷F_J (J = 1,2,3), and ⁵D₀ → ⁷F_J (J = 0, 1, 2, 3, 4) transitions. The higher level ⁵D_J (J = 1, 2, 3) emission depends on the concentration of Eu³⁺ ions. The emission spectra shows a completely different ratio between the ⁵D_3,2,1 blue-green emission and ⁵D₀ red emission for lower and higher Eu³⁺ concentrations. For lower Eu³⁺ ion concentrations, the dominant transition of Ca₂(La_1−xEu_x)TaO₆ phosphors are ⁵D_3,2,1,0 → ⁷F_J emissions, whereas the dominant transitions are ⁵D₀ → ⁷F_J emissions for higher Eu³⁺ ion concentrations. The chromaticity coordinate of the Ca₂(La_1−xEu_x)TaO₆ phosphor varies with the Eu³⁺-doped concentrations from white, to reddish orange, and red. Thus, this type of phosphor may be potentially applicable as a white light emitting phosphor for ultraviolet light-emitting diodes.     

Enhanced luminescence properties of YBO3:Eu phosphors by Li-doping

Different concentrations of Li-doped YBO₃:Eu³⁺ phosphors have been prepared by the conventional solid state reaction method and were characterized by X-ray diffraction, field emission scanning electron microscopy, photoluminescence excitation and emission measurements. An intense reddish orange emission is observed under UV excitation and the emitted radiation was dominated by an orange peak at 594 nm resulted from the ⁵D₀ → ⁷F₁ transitions of Eu³⁺ ions. The brightness of the YBO₃:Eu³⁺ phosphor was found greatly improved with Li-doping accompanied by slight improvement in the purity of the color which might be attributed to improvement in crystallinity, grain sizes and creation of oxygen vacancies with Li-doping. The observed results have been discussed in comparison with similar reported works.     

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.     

A novel red emitting phosphor CaIn2O4:Eu, Sm with a broadened near-ultraviolet absorption band for solid-state lighting

Red phosphor of CaIn₂O₄:Eu³⁺, Sm³⁺ is synthesized by solid state reaction. The ⁵D₀ → ⁷F₂ transition of Eu³⁺ is dominantly observed in the photoluminescence spectrum, leading to a red emission of the phosphor. The doped Sm³⁺ is found to be efficient to sensitize the emission of Eu³⁺ and be effective to extend and strengthen the absorption of near-UV light with wavelength of 400-405 nm, and the energy transfer from Sm³⁺ to Eu³⁺ occurs and is discussed. The effect of the molar concentration of Sm³⁺ on the emission intensities of the phosphor CaIn₂O₄:Eu³⁺, Sm³⁺ is investigated. The temperature quenching effect is also measured from room temperature to 425 K, and the emission intensity of the phosphor at 425 K shows about 85% of that at room temperature. Furthermore, the chromaticity coordinates, the emission intensities and the conversion efficiencies of CaIn₂O₄:Eu³⁺, Sm³⁺ are compared to those of the conventional red phosphor of Y₂O₂S:Eu³⁺.     

Preparation, characterization and luminescence of La2TeO6 phosphor doped with Eu

Phosphors of La₂TeO₆ doped with Eu³⁺ ions have been synthesized by the oxidation of the corresponding rare-earths oxytellurides of formula La_2−xEu_xO₂Te (x = 0.02, 0.06, and 0.1) at 1050 K. Powder X-ray diffraction confirms that the as prepared materials consist of the orthorhombic La₂TeO₆ as main phase. The photoluminescence (PL) of red-emitting La_2−xEu_xTeO₆ powder phosphors is reported. The emission spectrum, exhibits an intense emission peak due to ⁵D₀ → ⁷F₂ transition at 616 nm, which indicates that the Eu³⁺ ion occupies a non-centrosymmetric site in the host lattice. These materials could find application for use as lamp phosphors in the red region.     

Luminescence properties of Eu ions doped in Y2−xGdxO3 thin films grown by pulsed laser deposition method

Luminescence properties of Y_2−xGd_xO₃:Eu³⁺ (x = 0 to 2.0) thin films are investigated by site-selective laser excitation spectroscopy. The films were grown by pulsed laser deposition method on SiO₂ (100) substrates. Cubic phase Y₂O₃ and Gd₂O₃ and monoclinic phase Gd₂O₃ are identified in the excitation spectrum of the ⁷F₀ → ⁵D₀ transition of Eu³⁺. The emission spectra of the ⁵D₀ → ⁷F_J (J = 1 and 2) transition from individual Eu³⁺ centers were obtained by tuning the laser to resonance with each excitation line. The excitation line at around 580.60 nm corresponds to the line from Eu³⁺ with C₂ site symmetry of cubic phase. New lines at 578.65 and 582.02 nm for the C_S sites of Gd₂O₃ with monoclinic phase are observed by the incorporation of Gd in Y₂O₃ lattice. Energy transfer occurs between Eu³⁺ ions at the C_S sites and from Eu³⁺ ions at the C_S sites to those at the C₂ site in Y_2−xGd_xO₃.     

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.     

Formation and spectral probing of transparent oxyfluoride glass-ceramics containing (Eu2+, Eu3+:BaGdF5) nano-crystals

In the present study, we report the formation of transparent glass-ceramics containing BaGdF₅ nanocrystals under optimum ceramization of SiO₂–BaF₂–K₂O–Sb₂O₃–GdF₃–Eu₂O₃ based oxyfluoride glass and the energy transfer mechanisms in Eu²⁺ → Eu³⁺ and Gd³⁺ → Eu³⁺ has been interpreted through luminescence study. The modification of local environment surrounding dopant ion in glass and glass ceramics has been studied using Eu³⁺ ion as spectral probe. The optimum ceramization temperature was determined from the differential scanning calorimetry (DSC) thermogram which revealed that the glass transition temperature (T_g), the crystallization onset temperature (T_x), and crystallization peak temperature (T_p) are 563 °C, 607 °C and 641 °C, respectively. X-ray diffraction pattern of the glass-ceramics sample displayed the presence of cubic BaGdF₅ phase (JCPDS code: 24-0098). Transmission electron microscopy image of the glass-ceramics samples revealed homogeneous distribution of spherical fluoride nanocrystals ranging 5–15 nm in size. The emission transitions from the higher excited sates (⁵D_J, J = 1, 2, and 3) as well as lowered asymmetry ratio of the ⁵D₀ → ⁷F₂ transition (forced electric dipole transition) to that of the ⁵D₀ → ⁷F₁ transition (magnetic dipole) of Eu³⁺ in the glass-ceramics when compared to glass sample demonstrated the incorporation of dopant Eu³⁺ ions into the cubic BaGdF₅ nanocrystals with higher local symmetry with enhanced ionic nature. The presence of absorption bands of Eu²⁺ ions and Gd³⁺ ions present in the glass matrix or fluoride nanocrystals in the excitation spectra of Eu³⁺ by monitoring emission at 614 nm indicated energy transfer from (Eu²⁺ → Eu³⁺) and (Gd³⁺ → Eu³⁺) in both glass and glass-ceramics samples.     

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.     

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.     

Upconversion luminescence of Ho sensitized by Yb in transparent glass ceramic embedding BaYF5 nanocrystals

Transparent SiO₂-Al₂O₃-BaCO₃-YF₃-BaF₂ glass ceramics co-doped with Yb³⁺/Ho³⁺ ions were prepared by melt quenching and subsequent heating. X-ray diffraction and transmission electron microscopy observation revealed that BaYF₅ nanocrystals incorporated with Yb³⁺ and Ho³⁺ were precipitated homogeneously among the oxide glass matrix. Three upconversion emission bands centered at 483 nm, 545 nm and 645 nm, corresponding to the ⁵F₃ → ⁵I₈, ⁵S₂, ⁵F₄ → ⁵I₈ and ⁵F₅ → ⁵I₈ transitions of Ho³⁺ respectively, were detected under 976 nm excitation, ascribing to the efficient energy transfer from Yb³⁺ to Ho³⁺. The red emission is prevailing in the precursor glass, while the green one turns to be dominant in the glass ceramic.