Lu2O3 Powders Research Articles

Effect of Raw Material on the Properties of LuAG:Cr4+ Ceramics

Samples of Cr4+:LuAG ceramics have been synthesized using commercial and reprecipitated Lu2O3 powders. The optimum conditions for the synthesis of the reprecipitated Lu2O3 powder have been established, a dilatometric analysis of the ceramics has been carried out, and the effect of the initial Lu2O3 powder on the optical properties of the ceramics has been studied.

Efficiency degradation of laser ceramics caused by inappropriate dispersants and sintering aids

Lasing quality 8 at.% Yb:Lu2O3 laser ceramics were fabricated using nanocrystalline Yb:Lu2O3 powders synthesized with a modified coprecipitation method and either (NH4)2SO4 or PAA (Poly acrylic acid) as a dispersant. Although using (NH4)2SO4 as a dispersant the calcinated Yb:Lu2O3 powders could have better sinterability, and the sintered Yb:Lu2O3 ceramics could even have higher in-line transmittance, it was found that the laser ceramics always had much lower lasing efficiency than those fabricated with PAA as a dispersant. We show that the efficiency degradation of the laser ceramics is due to the photodarkening caused by using (NH4)2SO4 as a dispersant.

Synthesis and physicochemical characterization of Lu and Sm sesquioxide nanoparticles by precipitation-calcination and pulsed laser ablation in liquids

This study synthesized peptide-functionalized Lu and Sm sesquioxide nanoparticles by precipitation-calcination (P–C) and pulsed laser ablation in liquids (PLAL) to evaluate their physicochemical properties after neutron activation. Nanoparticles were obtained by precipitation in an alkaline solution, followed by centrifugation, drying, calcination, and functionalization with peptides (three or eighteen amino acids). For the PLAL nanoparticle synthesis, tablets made of Lu2O3 and Sm2O3 powders were immersed in peptide solutions and laser-irradiated (Nd:YAG) for 30 min, followed by ultracentrifugation as a purification process. The nanosystems were analyzed using transmission electron microscopy, high-resolution transmission electron microscopy, selected area electron diffraction, X-ray diffraction, differential scanning calorimetry-thermogravimetry, and FTIR and UV–Vis spectroscopies. Luminescence was evaluated after nanoparticle neutron activation using an optical imaging device (CCD camera). The Lu2O3 and Sm2O3 nanoparticles synthesized by P–C showed a quasi-spherical and well-defined morphology, with a monomodal and monodispersed size distribution (30.05–44.83 nm) and highly crystalline patterns (cubic m3‾ space group). In contrast, the micrographs of the Lu and Sm sesquioxide nanoparticles obtained by PLAL showed two distinct populations, namely, one of well-defined and dispersed spherical particles (62.35–75.02 nm), and the other of precursor material fragments without defined form or size (>2 μm). The diffractograms of the PLAL synthesis products were wide and not well defined due to the amorphous material that was simultaneously produced with the crystalline nanoparticles, which affected the detection of luminescence. The nanosystems prepared by P–C were obtained in high yields (70% for Lu2O3 and 90% for Sm2O3) and with optimal physicochemical characteristics, significantly impacting the radioluminescence properties of the nanoparticles (emissions of ∼615 nm for Lu2O3 and ∼758 nm for Sm2O3). P–C is a suitable method for producing peptide-functionalized [177Lu]Lu and [153Sm]Sm sesquioxide nanoparticles for dual imaging (nuclear and optical imaging) in potential theranostic applications.

Fabrication and electrical conductivity of Lu2(Ti1-x Hf x )2O7 transparent ceramics prepared by spark plasma sintering

ABSTRACT Lu2(Ti1-x Hf x )2O7 (x = 0–0.5) transparent ceramics were fabricated by reactive spark plasma sintering using commercially available Lu2O3, TiO2 and HfO2 powders. Effect of Hf content x on the phase evolution, microstructure, density, transmittance and electrical conductivity of the resulting ceramics were investigated. Lu2(Ti1-x Hf x )2O7 transparent ceramic had a pyrochlore structure in the range of x = 0–0.3, while preserved a defect-fluorite structure at x = 0.4–0.5. The lattice parameter and theoretical density increased linearly with increasing Hf content x. The average grain size decreased at x = 0–0.3 and kept almost constant at x = 0.4–0.5. All the samples exhibited a dense microstructure and the highest in-line transmittance was 57% at 550 nm at x = 0. The highest bulk conductivity was 1.7 × 10−2 S m−1 at 1073 K for Lu2(Ti0.8Hf0.2)2O7, with an activation energy of 1.16 eV.

Fabrication, microstructures, and optical properties of Yb:Lu2O3 laser ceramics from co-precipitated nano-powders

The Yb:Lu2O3 precursor made up of spherical particles was synthesized through the co-precipitation method in the water/ethanol solvent. The 5 at% Yb:Lu2O3 powder is in the cubic phase after calcination at 1100 °C for 4 h. The powder also consists of spherical nanoparticles with the average particle and grain sizes of 96 and 49 nm, respectively. The average grain size of the pre-sintered ceramic sample is 526 nm and that of the sample by hot isostatic pressing grows to 612 nm. The 1.0 mm-thick sample has an in-line transmittance of 81.6% (theoretical value of 82.2%) at 1100 nm. The largest absorption cross-section at 976 nm is 0.96×10−20 cm2 with the emission cross-section at 1033 nm of 0.92×10−20 cm2 and the gain cross sections are calculated with the smallest population inversion parameter β of 0.059. The highest slope efficiency of 68.7% with the optical efficiency of 65.1% is obtained at 1033.3 nm in quasi-continuous wave (QCW) pumping. In the case of continuous wave (CW) pumping, the highest slope efficiency is 61.0% with the optical efficiency of 54.1%. The obtained laser performance indicates that Yb:Lu2O3 ceramics have excellent resistance to thermal load stresses, which shows great potential in high-power solid-state laser applications.

Effective calcination pretreatment of Lu2O3 powders for LuAG transparent ceramics

Lutetium aluminium garnet (LuAG) ceramics as host materials has been widely used in lighting, laser, displaying and scintillators after doping different rare earth ions. Right selection of raw powder and controlling its characteristics during the preparation can greatly improve the optical quality of transparent ceramics. In this paper, the influence of different pretreatment temperatures of commercial Lu2O3 powders in oxygen atmosphere on solid state sintering of LuAG ceramics was systematically investigated. The pretreatment gradually decreased the specific surface area of Lu2O3 powders and greatly removed the absorbed impurities, which seriously deteriorated the optical quality before. The mean particle size increased from 4.53 to 5.66 μm, and the in-line transmittance of samples (Thickness = 2 mm) at 1064 nm was 68.4% for the pretreated Lu2O3 powder at 1000 °C without any sintering additives. Further increase of pretreatment temperature would lead to the coarsening of Lu2O3 powders and the decrease of sintering activity, which finally resulted in a large number of micro pores in LuAG ceramics. These results revealed that the pretreatment of Lu2O3 powders has prodigious impact on the optical quality of LuAG transparent ceramics, and the adsorbed materials should be removed as much as possible for their applications in lasers or lighting.

Dense ceramics of lanthanide-doped Lu2O3 prepared by spark plasma sintering

Dense ceramics of Ln:Lu2O3 (Ln = Pr, Eu, Tb, Dy) were obtained using spark plasma sintering (SPS) from co-precipitated nanocrystalline powders. X-ray diffraction, scanning and transmission electron microscopies were used for the characterization of Ln:Lu2O3 powders obtained by various annealing regimes. Transparency of the sintered ceramics was achieved when powders with highly developed crystallinity were used for sintering. Sintered ceramics exhibited luminescence with a characteristic emission based on the element doped into the Lu2O3 host. The light yield of the sintered ceramics improved when the sintered ceramics was further annealed. The annealing of the sintered ceramics also improved the transmittance in the visible region; however, the transparency was lost when the annealing temperature was too high. To our best knowledge, the SPS fabrication of dense ceramics of Pr3+, Tb3+ and Dy3+-doped Lu2O3 is reported here for the first time.

Fabrication of Lu2Ti2O7-Lu3NbO7 solid solution transparent ceramics by spark plasma sintering and their electrical conductivities

The Lu2Ti2O7-Lu3NbO7 system, belonging to A2B2O7 with a cubic structure, is attractive for tailored properties by substitution. In this study, Lu2+0.25xTi2−0.5xNb0.25xO7 (x = 0–4) transparent ceramics were fabrication by reactive spark plasma sintering using commercially available Lu2O3, TiO2 and Nb2O5 powders. The phase evolution, microstructure, density, transmittance and electrical conductivity were investigated as a function of composition parameter x. The results showed that Lu2+0.25xTi2−0.5xNb0.25xO7 transparent ceramic had a pyrochlore structure at x = 0 and 1, while preserved a defect-fluorite structure at x = 2–4. The lattice parameter and theoretical density increased linearly, while the average grain size decreased steadily with increasing composition parameter x. All the specimens exhibited a dense microstructure and the highest in-line transmittance was 64% at 550 nm for x = 4. The bulk conductivity increased with increasing x, reaching a maximum value of 4.2 × 10−2 S m-1 for Lu3NbO7 at 1073 K.

Crystal structure of lutetium aluminate (LUAM), Lu4Al2O9.

The crystal structure of the title compound containing lutetium, the last element in the lanthanide series, was determined using a single crystal prepared by heating a pressed pellet of a 2:1 molar ratio mixture of Lu2O3 and Al2O3 powders in an Ar atmosphere at 2173 K for 4 h. Lu4Al2O9 is isostructural with Eu4Al2O9 and composed of Al2O7 di-tetra-hedra and Lu-centered six- and sevenfold oxygen polyhedra. The unit-cell volume, 787.3 (3) Å3, is the smallest among the volumes of the rare-earth (RE) aluminates, RE 4Al2O9. The crystal studied was refined as a two-component pseudo-merohedric twin.

Synthesis of highly sinterable Yb:Lu2O3 nanopowders via spray co-precipitation for transparent ceramics

Abstract Highly sinterable Yb:Lu2O3 nano-powders without hard agglomeration were synthesized via a highly efficient spray co-precipitation method. The effects of the spray speeds on morphology and composition of the powders were investigated. The results showed that the composition and dispersion of precursor powders changed with the spray speed. When the spray speed reached 40 mL/min, the particles were spherical and showed higher uniformity. The pure phase Yb:Lu2O3 powder was obtained after calcining at 1000 °C for 2 h. The calcined powders were ball milled and dry-formed to prepare green body. Then the Yb:Lu2O3 transparent ceramic was fabricated by vacuum sintering at 1500 °C for 8 h and further hot isostatic pressing in an argon atmosphere.. The in-line optical transmittance of Yb:Lu2O3 transparent ceramic reached 82.05%@1000 nm and 81.08%@400 nm, respectively, and it had submicron level average grain size, which is an effective way to improve the optical properties of the transparent ceramic.

Fabrication, microstructure and spectroscopic properties of Yb:Lu2O3 transparent ceramics from co-precipitated nanopowders

Ytterbium doped lutetium oxide (Yb:Lu2O3) transparent ceramics were fabricated by vacuum sintering combined with hot isostatic pressing (HIP) of the powders synthesized by the co-precipitation method. The effects of calcination temperature on the composition and morphology of the powders were investigated. Fine and well dispersed 5 at% Yb:Lu2O3 powders with the mean particle size of 67 nm were obtained when calcined at 1100 °C for 4 h. Using the synthesized powders as starting material, we fabricated 5 at% Yb:Lu2O3 ceramics by pre-sintering at different temperatures combined with HIP post-treatment. The influence of pre-sintering temperature on the densities, microstructures and optical quality of the 5 at% Yb:Lu2O3 ceramics was studied. The ceramic sample pre-sintered at 1500 °C for 2 h with HIP post-treating at 1700 °C for 8 h has the highest in-line transmittance of 78.2% at 1100 nm and the average grain size of 2.6 µm. In addition, the absorption and emission cross sections of the 5 at% Yb:Lu2O3 ceramics were also calculated.

Self-propagating high-temperature synthesis of Lu2O3 powders for optical ceramics

A technique has been developed for the self-propagating high-temperature synthesis of lutetium oxide (Lu2O3) powders using citric acid, glycine, and lutetium acetate as fuels. We have carried out thermodynamic analysis of synthesis conditions and examined the effect of the nature of the fuel on the properties of the resultant powders. Using vacuum sintering at a temperature of 1780°C and powders prepared with glycine as a fuel and containing 25 mol % yttrium oxide and 5 mol % lanthanum oxide as sintering aids, we have obtained transparent lutetium oxide-based ceramics.

Investigation of the Energy-Transfer Mechanism in Ho3+- and Yb3+-Codoped Lu2O3 Phosphor with Efficient Near-Infrared Downconversion

A high-temperature solid-state method was used to synthesize the Ho3+- and Yb3+-codoped cubic Lu2O3 powders. The crystal structures of the as-prepared powders were characterized by X-ray diffraction. The energy-transfer (ET) phenomenon between Ho3+ ions and Yb3+ ions was verified by the steady-state spectra including visible and near-infrared (NIR) regions. Beyond that, the decay curves were also measured to certify the existence of the ET process. The downconversion phenomena appeared when the samples were excited by 446 nm wavelength corresponding to the transition of Ho3+: 5I8→5G6/5F1. On the basis of the analysis of the relationship between the initial transfer rate of Ho3+: 5F3 level and the Yb3+ doping concentration, it indicates that the ET from 5F3 state of Ho3+ ions to 2F5/2 state of Yb3+ ions is mainly through a two-step ET process, not the long-accepted cooperative ET process. In addition, a 62% ET efficiency can be achieved in Lu2O3: 1% Ho3+/30% Yb3+. Unlike the common situations in which the NIR photons are all emitted by the acceptors Yb3+, the sensitizers Ho3+ also make contributions to the NIR emission upon 446 nm wavelength excitation. Meanwhile, the 5I5→5I8 transition and 5F4/5S2→5I6 transition of Ho3+ as well as the 2F5/2→2F7/2 transition of Yb3+ match well with the optimal spectral response of crystalline silicon solar cells. The current research indicates that Lu2O3: Ho3+/Yb3+ is a promising material to improve conversion efficiency of crystalline silicon solar cell.

Influence of Eu3 + doping content on antioxidant properties of Lu2O3 sol-gel derived nanoparticles

This paper presents the synthesis of pure and europium-doped lutetium oxide (Lu2O3) powders prepared by sol-gel method. The influence of europium ion concentration into Lu2O3 nanocrystallites was investigated for first time in an in vitro system using a modified ABTS radical cation decolorization assay to determine the antioxidant activity. The crystalline structure of Lu2O3 and Eu:Lu2O3 powders was elucidated by XRD obtaining cubic phase in all system without secondary products in accordance with FT-IR results. By TEM and Scherrer equation, it was determined that Lu2O3 and Eu:Lu2O3 powders presented nearly spherical particle morphology with crystallites sizes in the range of 8 to 13nm. The antioxidant assays results revealed that europium ion enhance Lu2O3 powders antioxidant properties, showing that 12.5mol% of europium is sufficient to reach its maximum capacity.

Preparation and Photoluminescence Properties of Ti-Doped Lu2O3 Powder

Preparation and Photoluminescence Properties of Ti-Doped Lu2O3 Powder

Formation of high-density scintillation ceramic from LuAG:Ce + Lu2O3 powders obtained by co-precipitation method

The results of formation of the high density effective scintillation ceramics consisting of two compounds of the cubic symmetry, LuAG:Ce and Lu2O3 (LuAG:Ce+Lu2O3), are described. Powders of a novel material LuAG:Ce+Lu2O3 were synthesized by co-precipitation method. The introduction of Lu2O3 into LuAG:Ce was shown to increase the density of the ceramics obtained and modify its scintillation properties.

Sintering of transparent Yb-doped Lu2O3 ceramics using nanopowder produced by laser ablation method

Transparent Yb-doped Lu2O3 ceramic samples were fabricated via conventional vacuum and spark plasma sintering. Nanoparticles synthesized by laser ablation method were used as starting material. The morphology and phase evolution of the nanopowder were studied by transmission electron microscopy, simultaneous thermal analysis and X-ray diffraction. The obtained nanoparticles exhibited the monoclinic phase and were fully converted into the main cubic phase after calcination at 1100°C for 1h. Conventional vacuum sintering of Yb:Lu2O3 powder compact at 1780°C for 20h resulted in a fully-dense ceramics with an average grain size of 1.6μm and optical transmittance of 79.3% at 1080nm. Spark plasma sintering of the calcined Yb:Lu2O3 nanoparticles at 1450°C and 15kN for 40min led to a 0.2μm-grained ceramics exhibiting an optical transmittance of 75.6% at 1080nm.

Highly transparent ceramics obtained from jet milled sesquioxide powders synthesized by co-precipitation method

High purity Yb3+ doped Lu2O3 powder has been synthesized by the co-precipitation method. The powders underwent a jet milling at various feed rate using a commercial jet mill machine. It is found that jet milling is very effective in breaking up of large agglomerates without cross-contamination. Median agglomerate size decreased from 8.74 μm to 1.06 μm when jet milled at a feed rate 0.75 lb/hr. There was no noticeable increase in impurities picked up during the jet milling process in the final powder obtained after a sacrificial run that was carried out for the purpose of conditioning the surface of the liner. Homogeneous, uniform, and highly transparent ceramic was obtained from the ceramic hot pressed with the final jet milled powder compared to the one made from as-produced powder where some defects and splotches are often observed. Transmission of the Yb3+:Lu2O3 ceramics obtained from the jet milled powder is very close to the theoretical limit, demonstrating the excellent quality of the transparent ceramic.

Highly transparent Nd^3+:Lu_2O_3 produced by spark plasma sintering and its laser oscillation

Laser oscillation was demonstrated using a 1 at.% Nd3+-doped Lu2O3 (Nd3+:Lu2O3) transparent ceramic produced by spark plasma sintering. Nd2O3, Lu2O3, and LiF commercial powders were mixed by ball milling and were sintered at 1723 K using a two-step sintering profile. After the transparent Nd3+:Lu2O3 ceramic was annealed in air, its transmittance at 1076 nm reached 81.8%, which was close to the theoretical value for Lu2O3 (82.2%). The absorption cross-section at 806 nm was 1.29 × 10−20 cm2, and the fluorescence decay time at 1076 nm was 229 μs. The laser oscillation of Nd3+:Lu2O3 ceramic for the transition from 4F3/2 to 4I11/2—specifically, at 1076.7 and 1080.8 nm—was simultaneously obtained, with a laser output of 0.21 W and slope efficiency of 14%.

Fabrication and microstructure of cerium doped lutetium aluminum garnet (Ce:LuAG) transparent ceramics by solid-state reaction method

Polycrystalline Ce3+ doped lutetium aluminum garnet (Ce:LuAG) transparent ceramics fabricated by one step solid-state reaction method using synthetic nano-sized Lu2O3, commercial α-Al2O3 and CeO2 powders were investigated in this paper. The green compacts shaped by the mixed powders were successfully densified into Ce:LuAG transparent ceramics after vacuum sintering at 1750°C for 10h. The in-line optical transmittance of the Ce:LuAG ceramic made by home-made Lu2O3 powders could reach 57.48% at 550nm, which was higher than that of the ceramic made by commercial Lu2O3 powders (22.96%). The microstructure observation showed that light scattering centers caused by micro-pores, aluminum segregation and refraction index inhomogeneities induced the decrease of optical transparency of the Ce:LuAG ceramics, which should be removed and optimized in the future work.