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.     

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.     

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.     

The effect of Eu3+ concentration on the Y2O3 host lattice obtained from citrate precursors

This work presents a thermal decomposition study of the precursor resin prepared from the citrate precursor along with structural features and optical properties materials composed by Y₂O₃ and Eu³⁺ containing Y₂O₃ in 0.5, 3, 5 and 7 mol%. The microcrystallite sizes were estimated from the Scherrer equation. The structural and optical properties revealed that the addition of 5 mol% of Eu³⁺ to the Y₂O₃ matrix gave rise to the highest relative emission intensity which was evidenced by the luminescence intensity. The lifetime of the 0.5 mol% Eu³⁺-doped sample suggested two different symmetry sites for Eu³⁺ ions because two different lifetime values were acquired for this sample, while for phosphors doped with 3 or 5 mol% of Eu³⁺ ions only one similar lifetime was observed. When the concentration of Eu³⁺ is 0.5 and 3 mol%, the luminescence intensity is weak due to the low probability of the O^2? - Eu³⁺ charge transfer transition. On the other hand, when the concentration of the Eu³⁺ ions is 7 mol%, a quenching effect is evidenced.     

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.     

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.     

Infrared Luminescence of Y2O2S:Er3+ and Y2O3:Er3+

The diffuse reflectance and luminescence spectra of Y₂O₂S:Er³⁺ and Y₂O₃:Er³⁺ are studied under selective and polarized laser excitation. The results indicate that the Er³⁺ luminescence bands of yttrium oxysulfide in the 1.54-m region are one order of magnitude stronger and broader than those of yttria. Y₂O₂S:Er³⁺ is shown to contain two types of Er-related emission centers differing in the anion environment of the Er³⁺ ion.     

Synthesis and luminescence properties of red long-lasting phosphor Y2O2S:Eu3+, Mg2+, Ti4+ nanoparticles

We report an effective method to synthesize Y₂O₂S:Eu³⁺, Mg²⁺, Ti⁴⁺ nanoparticles. Tube-like Y(OH)₃ were firstly synthesized by hydrothermal method to serve as the precursor. Nanocrystalline long-lasting phosphor Y₂O₂S:Eu³⁺, Mg²⁺, Ti⁴⁺ was obtained by calcinating the precursor with co-activators and S powder. XRD investigation shows a pure phase of Y₂O₂S, indicating no other impurity phase appeared. SEM and TEM observation reveals that the precursor synthesized via a hydrothermal routine has tube-like structure and the final phosphor reveals a hexagonal shape. The fine nanoparticles which have the particle size ranging from 30 to 50 nm show uniform size and well-dispersed distribution. From the spectrum, the main emission peaks are ascribed to Eu³⁺ ions transition from ⁵D_J (J = 0, 1, 2) to ⁷F_J (J = 0, 1, 2, 3, 4). After irradiation by 325 nm for 10 min, the Y₂O₂S:Eu³⁺, Mg²⁺, Ti⁴⁺ long-lasting phosphor shows very bright red afterglow and the longest could last for more than 1 h even after the irradiation source had been removed. It is considered that the long-lasting phosphorescence is due to the contribution from the electron traps with suitable trap depth.     

Si3N4-ZrO2 composites with small Al2O3 and Y2O3 additions prepared by HIP

Si₃N₄-ZrO₂ composites have been prepared by hot isostatic pressing at 1550 and 1750 °C, using both unstabilized ZrO₂ and ZrO₂ stabilized with 3 mol% Y₂O₃. The composites were formed with a zirconia addition of 0, 5, 10, 15 and 20 wt%, with respect to the silicon nitride, together with 0–4 wt% Al₂O₃ and 0–6 wt% Y₂O₃. Composites prepared at 1550 °C contained substantial amounts of unreacted -Si₃N₄, and full density was achieved only when 1 wt% Al₂O₃ or 4 wt % Y₂O₃ had been added. These materials were generally harder and more brittle than those densified at the higher temperature. When the ZrO₂ starting powder was stabilized by Y₂O₃, fully dense Si₃N₄-ZrO₂ composites could be prepared at 1750 °C even without other oxide additives. Densification at 1750 °C resulted in the highest fracture toughness values. Several groups of materials densified at 1750 °C showed a good combination of Vickers hardness (HV10) and indentation fracture toughness; around 1450 kg mm^–2 and 4.5 MPam^1/2, respectively. Examples of such materials were either Si₃N₄ formed with an addition of 2–6 wt% Y₂O₃ or Si₃N₄-ZrO₂ composites with a simultaneous addition of 2–6 wt%Y₂O₃ and 2–4 wt% Al₂O₃.     

A facile preparation and the luminescent properties of Eu3+-doped Y2O2SO4 nanopieces

The europium(III)-doped yttrium oxysulfate (Y₂O₂SO₄:Eu³⁺) nanopieces have been prepared via electrospinning followed by calcination at 1000 °C in mixed gas of sulfur dioxide and air. Based on the experimental results, a possible formation mechanism for the nanopieces is that the nanopieces are determined by the directing template of electrospun nanoribbons and the multilayer crystal structure of Y₂O₂SO₄. Besides, the nanopieces show excellent luminescent properties with emissions at 581, 589, 597, 653, 619, and 697 nm resulting from the ⁵D₀ → ⁷F_J (J = 0, 1, 2, 3, 4) transition of Eu³⁺. The peaks of charge transfer and ⁵D₀ → ⁷F₂ transition of Eu³⁺ obviously have red shifts comparing to those of both Y₂O₃:Eu³⁺ nanoribbons and commercial Y₂O₃:Eu³⁺. Moreover, the nanopieces exhibit stronger intensities than the Y₂O₃:Eu³⁺ in excitation and emission spectra. Concentration quenching in the nanopieces occurs when Eu³⁺ concentration is 11 mol%, indicating that the nanopieces have an optimum luminescent intensity under this doping concentration.     

Photoluminescence properties of Eu2+-activated Ca2Y2Si2O9 phosphor

Eu²⁺-activated Ca₂Y₂Si₂O₉ phosphors with different Eu²⁺ concentrations have been prepared by a solid-state reaction method at high temperature and their photoluminescence (PL) properties were investigated. Photoluminescence results show that Eu²⁺-doped Ca₂Y₂Si₂O₉ can be efficiently excited by UV–visible light from 300 to 425 nm. Ca₂Y₂Si₂O₉: Eu²⁺ exhibits broad band emission in the wavelength range of 425–700 nm, due to the 4f⁶5d¹ → 4f⁷5d⁰ transition of the Eu²⁺ ions located at two different sites ((Ca/Y)1 and (Ca/Y)2) in Ca₂Y₂Si₂O₉. The effect of the Eu²⁺ concentration in Ca₂Y₂Si₂O₉ on the PL properties was investigated in detail. The results showed that the relative PL intensity reaches a maximum at 1 mol% of Eu²⁺, and a red-shift of the emission bands from these two different sites was observed with increasing Eu²⁺ concentration. Also there exists energy transfer between these two Eu²⁺ sites. The potential applications of Ca₂Y₂Si₂O₉: Eu²⁺ have been pointed out.     

Hole burning in YSZ:Pr3+ and YSZ:Eu3+ with various Y2O3 concentration

We have measured the hole spectra in YSZ:Pr³⁺ and YSZ:Eu³⁺ with various Y₂O₃ concentrations at low temperature. The temperature dependence of the hole width which obtained from the hole spectra in YSZ:Pr³⁺ and YSZ:Eu³⁺ was similar to that for disordered materials.

However, the Y₂O₃ concentration dependence of the hole width in YSZ:Pr³⁺ was contrary to that for YSZ:Eu³⁺ at low temperature. The hole width was the widest in the case of YSZ:Pr³⁺ at 10 mol% Y₂O₃. On the contrary, it was the narrowest in the case of YSZ:Eu³⁺ at the same concentration of Y₂O₃. It was found that there are two states in YSZ, in which the degree of ordered differs from each other. Additionally, the Y₂O₃ concentration dependence of the hole width at low temperature has reflected the ionic conductivity of YSZ at high temperature. It is suggested that the ordering of local structure is responsible for the ionic conduction in YSZ.

© 2003 Elsevier Science Ltd. All rights reserved.     

Mechanical properties and microstructures of co-precipitation derived tetragonal Y2O3-ZrO2-Al2O3 composites

Y-TZP Al₂O₃ specimens (2.5 mol% Y₂O₃-ZrO₂ and 5 to 30 wt% Al₂ 03) were prepared from coprecipitated powders and their mechanical properties were studied. The addition of alumina to Y-TZP improves the attainable density of the materials after sintering at 1500° C and reduces the degradation of their densities due to porosity formation when the materials are sintered above 1500° C. Near theoretical density could be achieved for most of the samples after HIPing at 1500° C for 1/2 h at 200 M Pa pressure. The fracture strength of the HIPed specimens was in the range 2.0 to 2.4 GPa and the stress intensity factor was in the range 3.5 to 6.0 MPa m^1/2. The mechanical strength of the materials was not degraded seriously after autoclaving in water at 175° C for 24 h. The surface layer of transformed monoclinic zirconia was less than 70 m thick even after autoclaving at 175° C for 5 days.     

Zr-Hf interdiffusion in polycrystalline Y2O3-(Zr+Hf)O2

Lattice and grain-boundary interdiffusion coefficients were calculated from the concentration distributions determined for Zr-Hf interdiffusion in polycrystalline 16Y₂O₃·84(Zr_1–x Hf _x )O₂ withx=0.020 and 0.100. The lattice interdiffusion coefficients were described byD=0.031 exp [–391 (kJ mol^–1)/RT] cm² sec^–1 and the grain-boundary diffusion parameters byD=1.5×10^–6exp [–309(kJ mol^–1)/RT] cm³ sec^–1 in the temperature range 1584–2116° C. Comparison of the results with those for the systems CaO-(Zr+Hf)O₂ and MgO-(Zr+Hf)O₂ indicated that the Zr self-diffusion coefficient was insensitive to the dopants in the fluorite-cubic ZrO₂ solid solutions.     

Pressureless sintering of Y2O3-CeO2-doped sialons

Various sialon materials have been prepared by pressureless sintering at 1775 and 1825 °C using Y₂O₃ and/or Ce0₂ as sintering aids. Constant molar amounts of the oxide mixtures were added in the ratios Y₂O₃/CeO₂: 100/0, 75/25, 50/50, 25/75, 0/100 corresponding to 6.0 and 9.25 wt% for the pure Y₂O₃ and pure CeO₂, respectively. Only one of the compositional series reached full density at 1775 °C with cerium replacing yttrium, whereas at 1825 °C all compositional series except one became dense. The samples sintered showed that yttrium but not cerium stabilizes the sialon phase in these ceramics. The dense cerium-sialon ceramics sintered at 1825 °C have as good hardness and indentation fracture toughness as the corresponding yttrium-sialon ceramics, or even higher for the sialon type of materials. For the mixed - sialon materials the hardness decreased as the amount of a sialon phase decreased by increasing cerium-doping.     

Sintering and compensation effect of donor- and acceptor-codoped 3mol% Y2O3-ZrO2

Addition of 0.15–0.5 mol% acceptor oxide, Al₂O₃, to 3 mol% Y₂O₃-ZrO₂ results in enhanced densification at 1350 °C. The enhancement is accounted for by a liquid phase sintering mechanism. The addition of donor oxide, Ta₂O₅, of 0.15–2.5 mol % at 1300–1600 °C results in the destabilization of tetragonal (t-) phase and the decrease of final density in 3 mol% Y₂O₃-TZP (tetragonal ZrO₂ polycrystals). X-ray diffractometry (XRD) reveals that the Ta₂O₅-added 3 mol% Y₂O₃-ZrO₂ contains monoclinic (m-) ZrO₂ and a second phase of Ta₂Zr₆O₁₇. The decreasing in final density is attributed to the increase of m-ZrO₂ content. Complete destabilization of t-ZrO₂ to m-ZrO₂ in samples added with 2.5 mol% Ta₂O₅ is interpreted by the compensation effect based on donor- and acceptor-codoping defect chemistry.     

Crystallization kinetics and structural properties of nanocrystalline europium-yttrium-titanate (Eu0.5Y0.5)2Ti2O7

We present a versatile sol–gel approach for nanocrystalline (Eu_0.5Y_0.5)₂Ti₂O₇. We determined the crystallization kinetics of the nucleation and the nucleation mechanism. The crystallization temperature was 1050.1 ± 0.8 K, and the activation energy of crystallization was 605 kJ mol^?1. The nanocrystal growth started by homogenous nucleation with a constant nucleation rate, and the nanocrystal growth was limited by mass transfer through the phase boundary. The crystal structure of (Eu_0.5Y_0.5)₂Ti₂O₇ was refined from the powder diffraction data using the Rietveld method, and the results were compared with the data recorded for the isostructural compounds, Eu₂Ti₂O₇ and Y₂Ti₂O₇. We proved the existence of a single phase of (Eu_0.5Y_0.5)₂Ti₂O₇ and the regular distribution of Eu³⁺ and Y³⁺ ions inside the crystal lattice. The results provide key information regarding the crystallization properties and crystal structure of nanocrystalline (Eu_0.5Y_0.5)₂Ti₂O₇. This knowledge is necessary for preparing pure nanocrystalline powders with tailored structural properties that are suitable for photonic applications.     

Mixed-solvothermal synthesis and characterization of triangular prism-like Y2O3

In this paper, it was demonstrated that Y₂O₃ microprisms could be prepared by a mixed-solvothermal method with triethylene tetramine as precipitator and sequent heat treatment process. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopic (TEM) and high-resolution transmission electron microscopic (HRTEM) were used to characterize the products. The height of the Y₄O(OH)₉(NO₃) microprisms is about 1.2 μm and the length of the side of the bottom surface is about 0.6 μm. It was found that the composition of solvent, dosage of triethylene tetramine, reaction time and reaction temperature had great effect on the morphologies of the final products. The as-obtained product via solvothermal process, monoclinic yttrium oxide hydroxide nitrate, Y₄O(OH)₉(NO₃), could convert to Y₂O₃ with the same morphology after annealing at high temperatures. Eu³⁺ doped Y₂O₃ microprisms were also prepared and their photoluminescence (PL) properties were investigated. This method may be applied to prepare other rare earth oxides with complex structures.     

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.     

Sintering process of Y2O3-added Si3N4

The sintering process of Y₂O₃-added Si₃N₄ has been investigated by dilatometry and microstructural observations. Densification was promoted above 1440 ° C by the formation of eutectic melts in the Y₂O₃-SiO₂-Si₃N₄ triangle. However, the dilatometric curves indicated no shrinkage corresponding to the rearrangement process, despite liquid-phase sintering. The kinetic order for The Initial-stage sintering was 0.47 to 0.49. These values indicated that the phase-boundary reaction was rate controlling. The apparent activation energy (323 kJ mol^–1) was smaller than the dissociation energy for the Si-N bond (435 kJ mol^–1). ESR data and lattice strain indicated that the disordered crystalline structure of the Si₃N₄ starting powder promoted the reaction of Si₃N₄ with eutectic melts. After a period of initial-stage sintering, the formation of fibrous -Si₃N₄ grains resulted in interlocked structures to interrupt the densification.