A novel strategy to synthesize Gd2O2S:Eu3+ luminescent nanobelts via inheriting the morphology of precursor

Gd₂O₃:Eu³⁺ nanobelts were fabricated by calcination of the electrospun PVP/[Gd(NO₃)₃ + Eu(NO₃)₃] composite nanobelts. For the first time, Gd₂O₂S:Eu³⁺ nanobelts were successfully prepared via inheriting the morphology and sulfurization of the as-prepared Gd₂O₃:Eu³⁺ nanobelts precursor using sulfur powders as sulfur source by a double-crucible method we newly proposed. X-ray diffraction analysis indicated that Gd₂O₂S:Eu³⁺ nanobelts were pure hexagonal in structure with space group P \( \bar{3} \) m1. Scanning electron microscope analysis results showed that the width and thickness of the Gd₂O₂S:Eu³⁺ nanobelts were ca. 2.1 μm and 129 nm, respectively. Under the excitation of 330-nm ultraviolet light, Gd₂O₂S:Eu³⁺ nanobelts emitted red emissions of predominant peaks at 628 and 618 nm which were attributed to the ⁵D₀ → ⁷F₂ energy levels transitions of the Eu³⁺ ions. It was found that the optimum doping molar concentration of Eu³⁺ ions in Gd₂O₂S:Eu³⁺ nanobelts was 5 %. Possible formation and sulfurization mechanisms of Gd₂O₂S:Eu³⁺ nanobelts were also proposed. This new sulfurization technique is of great importance, not only can inherit the morphology of rare earth oxides, but also can fabricate pure-phase rare earth oxysulfides at low temperature compared with conventional sulfurization method.     

Synthesis and luminescence properties of monodisperse SiO2@SiO2:Eu3+ microspheres

Monodisperse core–shell structured SiO₂@SiO₂:Eu³⁺ microspheres were synthesized in a seeded growth way. In that way, a thin shell of Eu³⁺-doped silica was grown on the prepared monodisperse silica colloids. The samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectrometry (EDX), X-ray diffraction (XRD), Fourier transform infrared spectrum (FT-IR), thermal analysis (TGA-DSC) and photoluminescence (PL) spectroscopy. The results reveal that the SiO₂ spheres have been successfully coated by SiO₂:Eu³⁺ phosphors and the obtained SiO₂@SiO₂:Eu³⁺ particles have perfect spherical shape with narrow size distribution. Additionally, the monodisperse SiO₂@SiO₂:Eu³⁺ microspheres exhibit considerably strong photoluminescence (PL) of Eu³⁺ under the excitation of 393 nm compared with the SiO₂:Eu³⁺ samples with polydispersed or irregular shapes and sizes obtained by base-catalyzed Stöber method. Furthermore, the PL intensity increases with the increasing of Eu³⁺ concentration in SiO₂ microspheres shell, and concentration quenching occurs when Eu³⁺ concentration exceeds 5.0 mol%.     

Luminescence and crystallinity of flame-made Y2O3:Eu3+ nanoparticles

Cubic and/or monoclinic Y₂O₃:Eu³⁺ nanoparticles (10–50 nm) were made continuously without post-processing by single-step, flame spray pyrolysis (FSP). These particles were characterized by X-ray diffraction, nitrogen adsorption and transmission electron microscopy. Photoluminescence (PL) emission and time-resolved PL intensity decay were measured from these powders. The influence of particle size on PL was examined by annealing (at 700–1300°C for 10 h) as-prepared, initially monoclinic Y₂O₃:Eu³⁺ nanoparticles resulting in larger 0.025–1 μm, cubic Y₂O₃:Eu³⁺. The influence of europium (Eu³⁺) content (1–10 wt%) on sintering dynamics as well as optical properties of the resulting powders was investigated. Longer high-temperature particle residence time during FSP resulted in cubic nanoparticles with lower maximum PL intensity than measured by commercial micron-sized bulk Y₂O₃:Eu³⁺ phosphor powder. After annealing as-prepared 5 wt% Eu-doped Y₂O₃ particles at 900, 1100 and 1300°C for 10 h, the PL intensity increased as particle size increased and finally (at 1300°C) showed similar PL intensity as that of commercially available, bulk Y₂O₃:Eu³⁺ (5 μm particle size). Eu doping stabilized the monoclinic Y₂O₃ and shifted the monoclinic to cubic transition towards higher temperatures.     

Magnetic and luminescent properties of Fe3O4@Y2O3:Eu3+ nanocomposites

The multifunctional Fe₃O₄@Y₂O₃:Eu³⁺ nanocomposites were prepared by a facile solvothermal method with Fe₃O₄ nanoparticles as the core and europium-doped yttrium oxide (Y₂O₃:Eu³⁺) as the shell. It is shown that Fe₃O₄@Y₂O₃:Eu³⁺ nanocomposites have a strong photoluminescence and special saturation magnetization Ms of 6.1 emu/g at room temperature. The effects of the magnetic field on the luminescence intensities of the nanocomposites are being discussed. The multifunctional nanocomposites with magnetic resonance response and fluorescence probe properties may be useful in biomedical applications, such as cell separation and bioimaging.     

Luminescence of SrGdGa3O7:RE(RE = Eu, Tb) phosphors and energy transfer from Gd to RE

Eu³⁺- and Tb³⁺-activated SrGdGa₃O₇ phosphors were synthesized by the solid-state reaction and their luminescence properties were investigated. Sr(Gd_1 − xEu_x)Ga₃O₇ and Sr(Gd_1 − xTb_x)Ga₃O₇ formed continuous solid solution in the range of x = 0-1.0. Unactivated SrGdGa₃O₇ exhibited a typical characteristic excitation and emission of Gd ion. The SrGdGa₃O₇:xEu³⁺ and SrGdGa₃O₇:xTb³⁺ phosphors also showed the well-known Eu³⁺ and Tb³⁺ excitation and emission. The energy transfer from Gd³⁺ to Eu³⁺ and Tb³⁺ were verified by photoluminescence spectra. The dependence of photoluminescence intensity on Eu³⁺ and Tb³⁺ concentration were also studied in detail and the photoluminescence (PL) intensity of SrGdGa₃O₇:Eu and SrGdGa₃O₇:Tb were compared with commercial phosphors, Y₂O₃:Eu and LaPO₄:Ce,Tb. The luminescence decay measurements showed that the lifetimes of Eu³⁺ and Tb³⁺ were in the range of microsecond. The energy transfer from Gd³⁺ to Tb³⁺ was also observed in decay curve.     

Synthesis of Y2O2S:Eu3+, Mg2+, Ti4+ hollow microspheres via homogeneous precipitation route

Abstract

A phosphorescent material in the form of Y₂O₂S:Eu³⁺, Mg²⁺, Ti⁴⁺ hollow microspheres was prepared by homogeneous precipitation using monodispersed carbon spheres as hard templates. Y₂O₃:Eu³⁺ hollow microspheres were first synthesized to serve as the precursor. Y₂O₂S:Eu³⁺, Mg²⁺, Ti⁴⁺ powders were obtained by calcinating the precursor in a CS₂ atmosphere. The crystal structure, morphology and optical properties of the composites were characterized. X-ray diffraction measurements confirmed the purity of the Y₂O₂S phase. Electron microscopy observations revealed that the Y₂O₂S:Eu³⁺, Mg²⁺, Ti⁴⁺ particles inherited the hollow spherical shape from the precursor after being calcined in a CS₂ atmosphere and that they had a diameter of 350–450 nm and a wall thickness of about 50–80 nm. After ultraviolet radiation at 265 or 325 nm for 5 min, the particles emitted strong red long-lifetime phosphorescence originating from Eu³⁺ ions. This phosphorescence is associated with the trapping of charge carriers by Ti⁴⁺ and Mg²⁺ ions.     

Luminescent properties of Ca2MgSi2O7 phosphor activated by Eu2+, Dy3+ and Nd3+

Long lasting alkaline earth silicates, Ca₂MgSi₂O₇:Eu,Dy,Nd was prepared under a reduction atmosphere through solid state reaction. The obtained phosphor was characterized by means of X-ray diffraction (XRD) and photoluminescence spectrum (PLS). The crystal structure of Ca₂MgSi₂O₇:Eu,Dy,Nd phosphor was refined by Rietveld analysis. The obtained Ca₂MgSi₂O₇:Eu,Dy,Nd phosphor showed a yellow–green emission peaking at 518 nm, which is ascribed to the luminescent emission of the Eu²⁺ that occupied the octa-coordinated Ca²⁺ sites in the Ca₂MgSi₂O₇ host. The electron affinity (ea) value for Eu²⁺ in [EuO₈] was calculated to 1.9 eV. The decay profile and the emission spectrum indicated that when the value of Dy/Eu is increasing, there is a concentration quenching of Eu²⁺.     

Photoluminescence properties and the self-reduction process of CaAl2Si2O8:Eu phosphor

CaAl₂Si₂O₈:Eu anorthite phosphor was synthesized by the traditional solid state reaction. In the air-sintered phosphor, the Eu ions were partial self-reduced to Eu²⁺, which contributed to the observation of the blue (Eu²⁺) and the red (Eu³⁺) emission in CaAl₂Si₂O₈:Eu phosphor. To further investigate the photoluminescence properties and the self-reduction mechanism of CaAl₂Si₂O₈:Eu phosphor, the adjustment of the valence state of Eu ions by controllable approaches was studied. In addition, CaAl₂Si₂O₈:Eu phosphor shows a tunable emission from reddish to bluish region under ultraviolet excitation, which implies that it could be applied as potential phosphor for near ultraviolet light emitting diode.     

Gd2O3:Eu@mesoporous SiO2 bifunctional core-shell composites: Fluorescence label and drug release

A novel kind of core-shell nanocomposite Gd₂O₃:Eu³⁺@mesoporous SiO₂ was successfully fabricated, which consisted of a solvothermal synthesized Gd₂O₃:Eu³⁺ nanospheres core, a thin nonporous silica midterm layer and an ordered mesoporous silica shell. The XRD, SEM, TEM, FTIR, N₂ adsorption/desorption and PL spectra were employed to characterize the composites. The cytotoxicity of Gd₂O₃:Eu³⁺@mesoporous SiO₂ and Gd₂O₃:Eu³⁺ was assessed by the standard MTT assay. The composites had spherically monodisperse morphology and a narrow size distribution around 180 nm in diameter. Furthermore, they also demonstrated the strong photoluminescence of ⁵D₀-⁷F_J emissions. In addition, the composites exhibited good property of sustained drug release by using ibuprofen (IBU) as model drug in the drug delivery process. Therefore, the drug release process could be easily tracked and identified through photoluminescence. Overall, the present composites have potential significant biomedical application as ideal bifunctional materials.     

Inherently Eu2+/Eu3+ Codoped Sc2O3 Nanoparticles as High‐Performance Nanothermometers

Luminescent nanothermometers have shown competitive superiority for contactless and noninvasive temperature probing especially at the nanoscale. Herein, we report the inherently Eu²⁺/Eu³⁺ codoped Sc₂O₃ nanoparticles synthesized via a one‐step and controllable thermolysis reaction where Eu³⁺ is in‐situ reduced to Eu²⁺ by oleylamine. The stable luminescence emission of Eu³⁺ as internal standard and the sensitive response of Eu²⁺ emission to temperature as probe comprise a perfect ratiometric nanothermometer with wide‐range temperature probing (77–267 K), high repeatability (>99.94%), and high relative sensitivity (3.06% K^–1 at 267 K). The in situ reduction of Eu³⁺ to Eu²⁺ ensures both uniform distribution in the crystal lattice and simultaneous response upon light excitation of Eu²⁺/Eu³⁺. To widen this concept, Tb³⁺ is codoped as additional internal reference for tunable temperature probing range.     

VUV-UV photoluminescence,site occupancy and thermal stability of blue-emitting K2CaP2O7:Eu2+ UV-LED phosphor

Blue-emitting phosphors K₂Ca_1?xP₂O₇:xEu²⁺ (x?=?0.005; 0.010; 0.015) were prepared by a solid-state reaction. The luminescence properties of the phosphors were systematically investigated. VUV photoluminescence spectra of K₂Ca_1?xP₂O₇:xEu²⁺ exhibit that three distinct bands peaking at 439, 478 and 535 nm can be attributed to the overlap of Eu(1), Eu(2) and Eu(3) emission bands, which are ascribed to the 4f–5d transition of Eu²⁺. The critical quenching concentration of Eu²⁺ in K₂CaP₂O₇ phosphor is about 1 mol%, and the critical transfer distance was determined to be 32.23 Å. When the temperature turned up to 150 °C, the emission intensity of K₂Ca_0.99P₂O₇:0.01Eu²⁺ sample was 60% of the initial value at room temperature. The activation energy E_a was calculated to be 0.217 eV, which proved the good thermal stability of the phosphor. All the properties indicated that the K₂CaP₂O₇:Eu²⁺ is promising blue-emitting phosphor for application in LED-based lighting or display systems.

     

Luminescence enhancement of Y2O3:Eu and Y2SiO5:Ce,Tb core particles with SiO2 shells

This paper reports on the luminescence and microstructural features of oxide nano-crystalline (Y₂O₃:Eu³⁺) and submicron-sized (Y₂SiO₅:Ce³⁺,Tb³⁺) phosphor cores, produced by two different synthesis techniques, and subsequently coated by an inert shell of SiO₂ using a sol-gel process. The shells mitigate the detrimental effect of the phosphor particle surfaces on the photoluminescence emission properties, thereby increasing luminous output by 20-90%, depending on the core composition and shell thickness. For Y₂O₃:Eu³⁺, uniformly shaped, narrow particle size distribution core/shell particles were successfully fabricated. The photoluminescence emission intensity of core nanoparticles increased with increasing Eu³⁺ activator concentration and the luminescence emission intensity of the core/shell particles was 20-50% higher than that of the core particles alone. For Y₂SiO₅:Ce³⁺,Tb³⁺, the core/shell particles showed enhancement of the luminescence emission intensity of 35-90% that of the core particles, depending on the SiO₂ shell thickness.     

Preparation,structural and spectroscopic studies of (YxLu1−x)2O3:Eu3+ nanopowders

Lutetium and yttrium oxides are promising scintillating materials suitable for use in medical planar X-ray imaging and mammography. In this paper the procedure for preparation of europium doped mixed lutetium–yttrium oxide nanopowders using polymer complex solution synthesis method is presented. Detailed information on nanopowder phase, morphology and crystallinity are obtained using X-ray powder diffraction, SEM and TEM while optical properties are investigated by photoluminescence and radioluminescence measurements. Constituting nanoparticles are 20–40 nm in size, and have excellent structural ordering in cubic bixbyite-type. Unit cell parameter, ionic coordinates, crystal coherence size and microstrain are determined from Rietveld analysis. All powders show strong Eu³⁺-characteristic red emission, with an average ⁵D₀ emission lifetime of 1.5 ms. Radioluminescence efficiency is about 15% of the commercial micron-sized Gd₂O₂S:Eu³⁺ powder while negligible level of afterglow is found.     

Synthesis of Y2O2S:Eu3+, Mg2+, Ti4+ hollow microspheres via homogeneous precipitation route

A phosphorescent material in the form of Y₂O₂S:Eu³⁺, Mg²⁺, Ti⁴⁺ hollow microspheres was prepared by homogeneous precipitation using monodispersed carbon spheres as hard templates. Y₂O₃:Eu³⁺ hollow microspheres were first synthesized to serve as the precursor. Y₂O₂S:Eu³⁺, Mg²⁺, Ti⁴⁺ powders were obtained by calcinating the precursor in a CS₂ atmosphere. The crystal structure, morphology and optical properties of the composites were characterized. X-ray diffraction measurements confirmed the purity of the Y₂O₂S phase. Electron microscopy observations revealed that the Y₂O₂S:Eu³⁺, Mg²⁺, Ti⁴⁺ particles inherited the hollow spherical shape from the precursor after being calcined in a CS₂ atmosphere and that they had a diameter of 350–450 nm and a wall thickness of about 50–80 nm. After ultraviolet radiation at 265 or 325 nm for 5 min, the particles emitted strong red long-lifetime phosphorescence originating from Eu³⁺ ions. This phosphorescence is associated with the trapping of charge carriers by Ti⁴⁺ and Mg²⁺ ions.     

Structural transition induced by the release of residual stress in the complex of cubic and monoclinic Gd2O3:Eu nanoparticles

The Photoluminescence (PL) spectra of Gd₂O₃:Eu composed of cubic and monoclinic structure were collected on November 2003 and June 2006, respectively. The results show that a portion of cubic Gd₂O₃ transforms into monoclinic after the sample was left as it is for two years; and the ⁵D₁-⁷F_J emission of Eu³⁺ in cubic host was enhanced in this released complex. Considering the high pressure behavior of Gd₂O₃, we think this structural transition is due to the sample that endures a process of press and release while the residual stress is released slowly.     

Synthesis of Y2O2S:Eu3+ luminescent nanobelts via electrospinning combined with sulfurization technique

Y₂O₂S:Eu³⁺ nanobelts were successfully prepared via electrospinning method and sulfurization process using the as-prepared Y₂O₃:Eu³⁺ nanobelts and sulfur powders as sulfur source by a double-crucible method for the first time. X-ray diffraction analysis indicated that the Y₂O₂S:Eu³⁺ nanobelts were pure hexagonal in structure with space group P $ \bar{3} $ m1. Scanning electron microscope images showed that the width and thickness of the Y₂O₂S:Eu³⁺ nanobelts were ca. 6.7 μm and 125 nm, respectively. Under the excitation of 325-nm ultraviolet light, Y₂O₂S:Eu³⁺ nanobelts exhibited red emissions of predominant peaks at 628 and 618 nm, which are attributed to the ⁵D₀ → ⁷F₂ transition of the Eu³⁺ ions. It was found that the optimum doping concentration of Eu³⁺ ions in the Y₂O₂S: Eu³⁺ nanobelts was 3 %. Compared with bulk particle, Eu³⁺–O^2?/S^2? charge transfer bands (260 and 325 nm) of the Y₂O₂S:Eu³⁺ nanobelts showed a blue-shift significantly. The formation mechanism of the Y₂O₂S: Eu³⁺ nanobelts was also proposed. This new sulfurization technique is of great importance, not only to inherit the morphology of rare earth oxides but also to fabricate pure-phase rare earth oxysulfides at low temperature compared with conventional sulfurization method.     

Synthesis and characterization Y2O3:Eu3+ nanocrystals prepared via solvothermal refluxing route

Y₂O₃:Eu³⁺ nanocrystals were prepared via co-precipitation–solvothermal refluxing–calcination method using three kinds of organic solvents, propylene glycol, 1,3-butanediol and polyethylene glycol and yttrium chloride hexahydrate and europium chloride as starting materials. The Y₂O₃:Eu³⁺ nanocrystals with diameter of 20–50 nm prepared by refluxing in polyethylene glycol followed by calcinations at 800–1000 °C exhibited the strongest luminescence at 611 nm under the excitation wavelength of 254 nm than the reference sample prepared via conventional co-precipitation method. The photoluminescence spectra of the samples were recorded at room temperature. The effect of concentration of Eu³⁺ (Eu³⁺/Y³⁺ atomic ratio: 0.01–0.1) on the photoluminescence intensity was also investigated. The samples with the Eu³⁺/Y³⁺ atomic ratio of 0.07 exhibited the strongest emission at 611 nm and quenching effect was observed above 0.10.     

Powder synthesis and white light-emitting properties of Eu3+ co-doped K2CaP2O7:Dy3+ phosphors with energy transfer between Dy3+ and Eu3+

A series of white-emitting K₂CaP₂O₇:Dy³⁺ and K₂CaP₂O₇:Dy³⁺, Eu³⁺ phosphors were synthesized via a solid-state method, and Eu³⁺ was co-doped in K₂CaP₂O₇:Dy³⁺ to improve its white light performance. The influences of preparation temperature and Dy³⁺/Eu³⁺ concentration on the crystal structure and photoluminescence characteristics were investigated. XRD results indicate that K₂CaP₂O₇:Dy³⁺ samples prepared above 700 °C matches the standard K₂CaP₂O₇ phase. Under excitation of 349 nm, K₂CaP₂O₇:Dy³⁺ phosphor exhibited characteristic emission peaks at 487 nm (blue) and 579 nm (yellow), and white emission was realized through combining these blue and yellow emissions. After co-doping Eu³⁺ ions, the co-luminescence of Dy³⁺/Eu³⁺ with energy transfer between Dy³⁺and Eu³⁺ were demonstrated. The chromaticity of white light was controlled by changing the ratio of Dy³⁺/Eu³⁺ concentrations, which lead to a warm white light. Therefore, the results indicate that K₂CaP₂O₇:Dy³⁺, Eu³⁺ powders have a potential application in w-LEDs as single-component white-emitting phosphor.     

Tunable color emitting of CaAl2Si2O8: Eu,Tb phosphors for light emitting diodes based on energy transfer

A series of single-phased CaAl₂Si₂O₈: Eu, Tb phosphors have been synthesized at 1400 °C via a solid state reaction. The emission bands of Eu²⁺ and Eu³⁺ were observed in the air-sintered CaAl₂Si₂O₈: Eu phosphor due to the self-reduction effect. Tb³⁺ ions that typically generated green emission were added in CaAl₂Si₂O₈: Eu phosphor for contributing for a wider-range tunable emission. Energy transfer from Eu²⁺ to Tb³⁺ and the modulation of valence distribution of Eu²⁺/Eu³⁺ that contributes to the tunable color emitting were elucidated. More importantly, a white emission can be obtained by controlling the codoped contents of Li⁺ as well as suppressing the self-reduction degree of Eu. The white light emitting with the color coordinate (0.326, 0.261) was obtained, which indicates that CaAl₂Si₂O₈: Eu, Tb is a promising tunable color phosphor for application in ultraviolet light emitting diodes (UV-LEDs).     

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.