Lu2O3 Nanopowders Research Articles

Study of densification mechanisms during Spark Plasma Sintering of co-precipitated Ho:Lu2O3 nanopowders: Application to transparent ceramics for lasers

This work was focused on the determination of densification mechanisms during Spark Plasma Sintering (SPS) of Ho:Lu2O3 nanopowders. Strong variation of the stress exponent n was evidenced during the sintering process. At low relative density (i.e. ρ < 66 %), n = 3 and powder particles rearrangement and coalescence take place because of high value of effective stress and low size of primary nanoparticles. Then, for ρ between 66 % and 85 %, the stress exponent decreases to n = 2 then n = 1. Such values were related to Rachinger then Lifshitz sliding mechanisms, the last one was associated with an average activation energy of 565 kJ.mol−1. At the final densification stage (ρ > 85 %), the stress exponent suddenly increases to 4 in accordance with a power-law creep. From these investigations, an optimized thermomechanical cycle was proposed to obtain highly transparent Ho:Lu2O3 ceramics suitable for laser applications.

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.

Submicron‐grained Yb:Lu2O3 transparent ceramics with lasing quality

AbstractWe report on our recent progress of fabricating Yb3+‐doped Lu2O3 transparent ceramics for 1 μm solid‐state laser application. Well‐dispersed 3.3 at.% Yb:Lu2O3 nanopowders were synthesized using a co‐precipitation method. Without using any sintering aids, the Yb:Lu2O3 nanopowders could be densified by vacuum sintering at 1500°C/10 hours followed by HIPing at 1480°C/4 hours. Such obtained Yb:Lu2O3 ceramics had not only dense microstructure and submicron grain size of about 0.6 μm, but also in‐line transmission of 80.0% at 600 nm. Preliminary continuous wave (CW) laser experiments with an uncoated Yb:Lu2O3 ceramic slab have demonstrated highly efficient CW laser oscillation at 1079.8 nm.

Effect of pH value on structural and photoluminescence properties of Tb3+ -doped Lu2O3 nanopowders synthesized by sol–gel route

Tb3+-doped Lu2O3 nanophosphors were prepared via simple sol–gel method, at different pH value of solution (2, 5, 8 and 11), using diethanolamine (DEA) as polymerization agent. The nanopowder samples were characterized by X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, room temperature steady and time resolved photoluminescence spectroscopy. The structural analysis reveals that all samples mainely crystallized in the cubic bixbyite structure with Ia3 space group. Also, it was found that the pH value of solution strongly influences the crystallite size, the vibrational frequency modes and the surface morphology of Lu2O3:Tb3+ nanocrystals. All samples show blue-greenish emissions, corresponding to 5D4 → 7FJ (J = 3, 4, 5 and 6) intraconfigurationnelles transitions. The intense green emission peak situated at 542 nm is assigned to 5D4 → 7F5 transition. The 4f8 → 4f75d1 spin-allowed and forbidden transitions, the charge transfer band (CTB) O2− → Tb3+ and the host absorption bands were observed and their dependence on pH value is discussed.

Synthesis of Er3+:Lu2O3 nanopowders by carbonate co-precipitation process and fabrication of transparent ceramics

Er3+ ions-doped Lu2O3 nanopowders were synthesized by co-precipitation method using NH4HCO3 as a precipitant, then Er3+:Lu2O3 transparent ceramics were fabricated by vacuum sintering using the as-prepared powder. The structure, crystallite size and upconversion luminescence (UCL) spectra of the as synthesized powders were characterized. The results indicated that the UCL properties of the powders varied with the calcination temperature and the Er3+ doping concentrations. Under the excitation of 980 nm laser diode, the ceramic sample showed a visually dominant green emission. Power studies revealed that the green (4S3/2 → 4I15/2) and red (4F9/2 → 4I15/2) upconversion emission of the sample occurred via a two-photon process.

Thermodynamic analysis of the self-propagating high-temperature synthesis of scandium and lutetium oxides nanopowders

Using the method of valence states of atoms in a chemical compound, we have calculated the standard enthalpies of formation for the reaction systems lutetium nitrate–lutetium acetate, scandium nitrate–scandium acetate, scandium nitrate–scandium acetylacetonate, and scandium nitrate–glycine. To optimize the composition of precursors for the self-propagating high-temperature synthesis of Sc2O3 and Lu2O3 nanopowders, we have analyzed the influence of the nature of the fuel and the oxidant to fuel ratio in the starting mixture on the adiabatic temperature and thermodynamically substantiated composition of reaction products.

Laser oscillation from Ho^3+ doped Lu_2O_3 ceramics

We report, for the first time, the laser oscillation from 2% Ho3+:Lu2O3 hot pressed ceramic. We have synthesized optical quality Lu2O3 nano-powders doped with concentrations as high as 5% Ho3+. The powders were synthesized by a co-precipitation method beginning with nitrates of holmium and lutetium. The nano-powders were hot pressed into optical quality ceramic discs. The optical transmission of the ceramic discs is excellent, nearly approaching the theoretical limit. The optical, spectral and morphological properties as well as the preliminary lasing performance from highly transparent ceramics are presented.

Synthesis of Er-doped Lu2O3 nanoparticles and transparent ceramics

Transparent rare earth-doped Lu2O3 ceramics have received much attention for use in solid-state scintillator and laser applications. The fabrication of these ceramics, however, requires ultrafine and uniform powders as precursors. Presented here is the synthesis of Er-doped Lu2O3 nanopowders by a solution precipitation method using Er-doped lutetium sulfate solution and hexamethylenetetramine as a precipitant and the fabrication of Er-doped Lu2O3 transparent ceramics from these nanopowders. The precipitated precursors were calcined at 1100°C for 4h in order to convert the precursors into Lu2O3 nanoparticles with an average particle size of 60nm. Thermal decomposition and phase evolution of the precursors were studied by simultaneous thermal analysis (STA), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). Er-doped Lu2O3 transparent ceramics were fabricated from these nanopowders using vacuum sintering followed by hot isostatic pressing at 1700°C for 8h. The transparent ceramics exhibit an optical transmittance of 78% at a wavelength of 1.55μm.

Tartaric acid-assisted co-precipitation synthesis of Er3+-doped Lu2O3 nanopowders

Abstract Erbium-doped lutetia nanopowders were synthesized by a novel co-precipitation method using tartaric acid as precipitant. The properties of the samples were investigated by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), TG-DSC, field emission scanning electron microscopy (FE-SEM), and upconversion luminescence analysis. Pure cubic Lu2O3 nanopowders were directly obtained when the precursor was calcined at 800 °C for 2 h, the samples showed strong upconversion luminescence under excitation of 980 nm laser diode.

Preparation and Scintillating Properties of Sol-Gel Eu3+, Tb3+ Co-Doped Lu2O3 Nanopowders

Nanocrystalline Eu3+, Tb3+ co-doped Lu2O3 powders with a maximum size of 25.5 nm were prepared by the sol-gel process, using lutetium, europium and terbium nitrates as precursors, and ethanol as a solvent. Differential thermal analysis (DTA) and infrared spectroscopy (IR) were used to study the chemical changes during the xerogel annealing. After the sol evaporation at 100 °C, the formed gel was annealed from 300 to 900 °C for 30 min under a rich O2 atmosphere, and the yielded product was analyzed by X-ray diffraction (XRD) to characterize the microstructural behavior and confirm the crystalline structure. The results showed that Lu2O3 nanopowders start to crystallize at 400 °C and that the crystallite size increases along with the annealing temperature. A transmission electron microscopy (TEM) study of samples annealed at 700 and 900 °C was carried out in order to analyze the microstructure, as well as the size, of crystallites. Finally, in regard to scintillating properties, Eu3+ dopant (5 mol%), Tb3+ codoped Lu2O3 exhibited a typical red emission at 611 nm (D°→7F2), furthermore, the effect of Tb3+ molar content (0.01, 0.015 and 0.02% mol) on the Eu3+ radioluminiscence was analyzed and it was found that the higher emission intensity corresponds to the lower Tb3+ content.