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The preparation of a well-dispersed, high solids content suspension is the foundation for colloidal forming methods to achieve ceramic green bodies with a uniformly microstructure, and meet the application requirements of various optical window materials. This article aims to enhance the dispersion stability of Y2 O3 suspension by utilizing the synergistic effect of two dispersants, namely triammonium citrate (TAC) and ammonium polyacrylate ( A40). The influence of the mixing ratio of two dispersants on the stability of Y2 O3 suspension and the microstructure of formed green bodies were mainly investigated, and the advantages of the dual dispersant system in improving the solid content and stability of Y2 O3 suspension were determined. The results show that the solid content of Y2O3 suspension could reach 38% (volume fraction) under the condition of TAC to A40 mass ratio of 7:3. A uniformly microstructure and densely packed particle was achieved. Y2 O3 transparent ceramics with a diameter of 9 mm and a thickness of 1 mm were obtained by vacuum sintering at 1 800°C, with a transmittance of 70. 34% at 800 nm. [ABSTRACT FROM AUTHOR]

Highly transparent Lu2O3 ceramics were prepared by using co‐precipitation combined with vacuum sintering method with ZrO2 as sintering aid. The effect of ZrO2 on densification, transmittance, and microstructure evolution of the Lu2O3 ceramics was carefully studied. It was found that the addition of ZrO2 was very effective in improving densification of Lu2O3. The highest transmittance (at 600 nm) of the 3 at.% ZrO2 doped Lu2O3 ceramic (1.6‐mm thickness) sintered at 1800°C reached 80.1%. Microstructural inhomogeneity was found after vacuum sintering with larger grain sizes at the central. The microstructural inhomogeneity mainly occurred in the final stage of sintering. Doping ZrO2 mitigated microstructural inhomogeneity and decreased markedly the grain size of Lu2O3 ceramics. Raman measurements indicated that the disordered structure was formed due to oxygen vacancy, and the oxygen vacancy concentration at the central was higher than at the peripheral. The oxygen vacancy concentration gradient is the dominant factor governing nonuniform microstructure evolution during vacuum sintering. Furthermore, a uniform microstructure was obtained by the inhibition of oxygen vacancy formation by the Lu2O3/ZrO2 double powder bed. [ABSTRACT FROM AUTHOR]

In the present work, Yb:YAG (yttrium aluminum garnet) transparent ceramics were fabricated using monodispersed spherical Y2O3, Al2O3 powders and commercial Yb2O3 nano-powder as raw materials, adding 0.5 wt% tetraethyl orthosilicae (TEOS) through the solid-state method and vacuum sintering technology. The prepared monodispersed Y2O3 and Al2O3 powders adopted by homogeneous co-precipitation showed improved mixing uniformity and lead to the reduced defect of the YAG powders. After sintering in vacuum at 1700 °C for 10 h, the (Y1−xYbx)AG (x = 0, 0.01, 0.10) ceramics with high transparency were obtained. Analysis of the densification rate, micromorphology, and optical properties of the ceramics suggests that the performance of the Yb:YAG ceramics is independent of the doping amount of Yb. Moreover, when the Y2O3, Al2O3, and Yb2O3 mixtures were laid aside for some time in the air after milling and drying, the performances of the as-prepared Yb:YAG ceramics would be affected distinctively. It is likely because the Y2O3 is easily hydrolyzed to Y(OH)3, Y(OH)2+ and Y2(OH)24+, which impinged the sintering activity of the powder mixture. [ABSTRACT FROM AUTHOR]

An easy approach is described for the preparation of ZrO2-coated Y2O3 nanopowder from a solution of zirconium nitrate with commercial Y2O3 nanopowder. The evolution process of the ZrO2 coating layer upon calcination, such as the phase and microstructure of the particles' surface, was studied. Calcination of the powder at 700 °C resulted in ZrO2-coated Y2O3 nanopowder. The rheological properties of the suspensions of ZrO2-coated Y2O3 powders were studied. A well-dispersed suspension with a solid loading of 35.0 vol% using ZrO2-coated Y2O3 nanopowder was obtained. The consolidated green body obtained by the centrifugal casting method showed improved homogeneity with a relative density of 50.2%. Transparent ceramic with high transparency and an average grain size of 1.7 µm was obtained by presintering at 1500 °C for 16 h in air, followed by post-HIP at 1550 °C for 2 h under 200 MPa pressure. The in-line transmittance at the wavelength of 1100 nm (1.0 mm thick) reached 81.4%, close to the theoretical transmittance of Y2O3 crystal. [ABSTRACT FROM AUTHOR]

An easy albeit quite effective deionization suspension treatment was adopted to alleviate the detrimental effects related to the hydrolysis of Y2O3 in an aqueous medium. Fabrication of highly transparent Y2O3 ceramics with a fine grain size via air pre‐sintering and post–hot isostatic pressing (HIP) treatment without using any sintering additive was achieved using the treated suspensions. The hydrolysis issue of Y2O3 powder in an aqueous medium was effectively alleviated by using deionization treatment, and a well‐dispersed suspension with a low concentration of dissolved Y3+ species was obtained. The dispersed suspensions were consolidated by the centrifugal casting method, and the green bodies derived from the suspension of 35.0 vol% solid loading showed an improved homogeneity with a relative density of 52.1%. Fully dense Y2O3 transparent ceramic with high transparency was obtained by pre‐sintering consolidated green compacts at a low temperature of 1400°C for 16 h in air followed by a post‐HIP treatment at 1550°C for 2 h under 200 MPa pressure. The sample had a fine average grain size of 690 nm. The in‐line transmittance of the sample reached 83.3% and 81.8% at 1100 nm and 800 nm, respectively, very close to the theoretical values of Y2O3. [ABSTRACT FROM AUTHOR]

Here, we proposed a groundbreaking strategy for fabricating YAG:Ce3+ transparent ceramic films via a novel interface reaction of LRH nanosheets with a sapphire substrate without a tedious process. The incorporation of Gd3+ greatly enhanced the emission intensity of the ceramic film by ∼11.3 times. The prepared transparent ceramic film with a high transmittance of ∼97% is a promising photo-converter for WLEDs. [ABSTRACT FROM AUTHOR]

A homogeneous co-precipitation method was developed to synthesize well dispersed yttrium aluminum garnet (YAG, Y 3 Al 5 O 12 ) powders. This method ensures the co-precipitation of Y 3+ and Al 3+ , solving the problem of differential precipitation of Y 3+ and Al 3+ in the conventional homogeneous precipitation method. Furthermore, the pH value can be controlled to be a plateau (around 5.2) during the titration process due to the continuous decomposition of the heated urea which can compensate for the pH reduction when adding the mother salts, which is beneficial to the narrow size distribution of the precipitates. Pure YAG nanopowders can be obtained at 900 °C without the formation of impurity phases such as YAM (Y 4 Al 2 O 9 ) or YAP (YAlO 3 ). The resultant YAG powders are well dispersed and have excellent sinterability that can be sintered into transparent ceramics at 1700 °C by vacuum sintering. [ABSTRACT FROM AUTHOR]

Monoclinic Gd2O3 transparent ceramics with spherical shape were successfully fabricated by a laser heating method. A simple model was used to describe the heating depth and cooling rate during the laser scanning process. The XRD analysis shows that these microspheres exhibit monoclinic structure which is room temperature thermodynamically unstable but kinetically possible due to the fast cooling rate. The SEM images show that these micro-spheres are polycrystalline and composed of randomly oriented Gd2O3 grains about 10 \mum in particle diameter. No cracks, pores or secondary phase were observed at the grain boundary or inside the grains. A close-packed Gd2O3 spheres single layer was designed and prepared, and the in-line transmittance of this layer is about 44% in the visible light range. Pore-free monoclinic Gd2O3 can be transparent due to the slight difference between its ordinary and extraordinary refractive index (ne and no). Another reason for its transparency is the small amount of grain boundaries though which light pass. Medical radiograph needs scintillators with small volume size (to increase the image lateral resolution and minimize optical cross-talking) and good transparency (to avoid severe light scattering and increase signal intensity). Transparent ceramic spheres may provide the possibility to meet those criterions. [ABSTRACT FROM PUBLISHER]

Highlights: [•] Stearate melting method can synthesize well dispersed fine YAG nanopowders. [•] The method ensures precise Y:Al ratio and cations mixing at atomic level. [•] Pure and dispersed YAG powders can be obtained at low temperature of 750°C. [•] The YAG powders can be sintered into transparent ceramics at 1700°C. [ABSTRACT FROM AUTHOR]

We show the effects of the Zr4+-doping on the microstructural, optical, and luminescent properties of (Lu, Gd) 2 O 3 : Eu transparent ceramics in its as-sintered state and annealed state. Zr4+-dopant greatly enhanced the transparency of (Lu, Gd) 2 O 3 : Eu ceramic, giving Lu 0.42 Gd 0.5 Zr 0.03 Eu 0.05 O 1.5+δ ceramic with a transmittance of up to 80% at 600 nm. It is found that Zr4+-dopant dominates the luminescent properties of Eu ions in both as-sintered and annealed ceramics. Energy transfer from Eu2+ to Eu3+ was found by photoluminescence spectra, and the ratio of Eu2+/(Eu2++Eu3+) was affected by Zr4+ content in as-sintered ceramics. Moreover, the oxygen vacancy concentration increased with increasing Zr4+ content in as-sintered ceramics. The annealing process enhanced the intensity of all the excitation bands of 4f→4f transitions and the intensity of charge transfer band (CTB) decreased as the Zr4+ content increased in the annealed ceramics. This work highlights that Zr4+ doping is a potential way to improve the transmittance and red emission intensity of 4f→4f transition of Eu3+ in the (Lu, Gd) 2 O 3 : Eu ceramic for extended applications. [ABSTRACT FROM AUTHOR]

Infrared transparent Ho: Y 2 O 3 -MgO nanocomposite ceramics with a volume ratio of 50:50 (RE 2 O 3 : MgO) were prepared by combining sol-gel powder synthesis and hot-pressing sintering techniques. In order to obtain Ho: Y 2 O 3 -MgO nanocomposite ceramics with fine grain size, dense microstructure and homogeneous phase domains, the effect of sintering temperature and Ho3+ doping concentration were studied. Transmittance and SEM measurement revealed that the grain size of 3 at.% Ho: Y 2 O 3 -MgO ceramic sintered at 1250 °C is 141 nm, and the transmission is up to 85.2% at 5 μm. The detailed spectroscopic investigation of x at.% Ho: Y 2 O 3 -MgO (x = 1, 3, 5, 7, 9, 15) ceramics was performed. The nanocomposites exhibited photoluminescence properties similar to that of Ho: Y 2 O 3 crystals and ceramics. In addition, the thermal conductivity of 3 at.% Ho: Y 2 O 3 -MgO ceramic is 13.04 W/m·K, which is superior to that of Ho:Y 2 O 3 ceramics. The high transmission, excellent thermal conductivity, and outstanding optical characteristics indicated that Ho: Y 2 O 3 -MgO ceramics is a promising material for efficient infrared solid-state laser. [ABSTRACT FROM AUTHOR]

• A new optical nanocomposite of Gd 2 O 3 -MgO was prepared by low-temperature hot-pressing. • Gd 2 O 3 -MgO nanopowders of with improved sinterabilty was obtained by elaborating Φ value. • Optical ceramics of Gd 2 O 3 -MgO nanocomposite has extremely fine-grain size of <95 nm. • The Gd 2 O 3 -MgO nanocomposite has IR-transparency of 80.3 %–84.7 % over 3−6 μm. • The Gd 2 O 3 -MgO nanocomposite exhibits a quite high hardness value of 14.3 ± 0.2 GPa. Refining ceramic microstructures to the nanometric range to minimize light scattering provides an interesting methodology for developing novel optical ceramic materials. In this work, we reported the fabrication and properties of a new nanocomposite optical ceramic of Gd 2 O 3 -MgO. The citric acid sol-gel combustion method was adopted to fabricate Gd 2 O 3 -MgO nanocomposites with fine-grain sizes, dense microstructures and homogeneous phase domains. Nanopowders with low agglomeration and improved sinterability can be obtained by elaborating Φ values. Further refining of the microstructure of the nanocomposites was achieved by elaborating the hot-pressing conditions. The sample sintered at 65 MPa and 1300 °C showed a quite high hardness value of 14.3 ± 0.2 GPa, a high transmittance of 80.3 %–84.7 % over the 3−6 μm wavelength range, due mainly to its extremely fine-grain size of Gd 2 O 3 and MgO (93 and 78 nm, respectively) and high density. [ABSTRACT FROM AUTHOR]

• Transparent Y 2 O 3 ceramics were prepared via colloidal processing method using ZrO 2 -coated nano-sized Y 2 O 3 powders. • The coating of ZrO 2 enhanced the absolute value of zeta potential in the pH > pH IEP range and pronouncedly decreased the viscosity of the Y 2 O 3 slurry. • The suspensions with low viscosity and high stability was achieved for a solid loading of 35.0 vol% using Y 2 O 3 powders coated with 5.0 at% ZrO 2. • The Y 2 O 3 ceramic sintered at 1800 ℃ shown the highest transmittance (at wavelength 800 nm, 1.0 mm thick) of 80.8%. In the present work, transparent Y 2 O 3 ceramics were prepared via colloidal processing method using ZrO 2 -coated nano-sized Y 2 O 3 powders. The chemical precipitation method was adopted for the coating of Y 2 O 3 raw powder. The evolution of the coated-ZrO 2 layer upon calcination was studied. The rheological behaviors of the slurries of Y 2 O 3 powders coated with different content of ZrO 2 -additive were investigated. The pH IEP of ZrO 2 -coated Y 2 O 3 powders shows intermediate values between that of raw Y 2 O 3 and ZrO 2 powders. As the ZrO 2 -coating concentration increased from 0 to 5.0 at%, the magnitude of the negative zeta potential at pH > pH IEP shows a general trend of increment, whereas it decreased at pH < pH IEP. The viscosity decreases pronouncedly with the increase of ZrO 2 content from 0.5 at% to 3.0 at%. The suspensions with low viscosity and high stability was achieved for a solid loading of 35.0 vol% using Y 2 O 3 powders coated with 5.0 at% ZrO 2. The dispersed suspensions were consolidated by centrifugal casting method and the green bodies shown improved homogeneity. Transparent Y 2 O 3 ceramics were fabricated by vacuum sintering at 1800 ℃ for 5 h. Transmittance at wavelength 800 nm (1.0 mm thick) reached 80.8%, close to the theoretical value of Y 2 O 3. [ABSTRACT FROM AUTHOR]

Yb:YAG (yttrium aluminum garnet) transparent ceramics were fabricated by the solid-state method using monodispersed spherical Y 2 O 3 powders as well as commercial Al 2 O 3 and Yb 2 O 3 powders. Pure YAG phase was obtained at low temperature due to homogeneous mixing of powders. Under the same sintering conditions, the Yb:YAG ceramics with different doping contents of Yb3+ had similar morphologies and densification rates. After being sintered at 1700 °C in vacuum, the ceramic samples had high transparencies. The Yb:YAG ceramics doped with 0.5 wt% SiO 2 formed Y–Si–O liquid phase and nonstoichiometric point defects that enhanced sintering. Compared with Nd doping, Yb doping hardly affected the YAG grain growth, sintering densification or optical transmittance, probably because Yb3+ easily entered the YAG lattice and had a high segregation coefficient. [ABSTRACT FROM AUTHOR]

Abstract Fine and dispersed (Y 1−x Ce x) 3 Al 5 O 12 (x = 0.005–0.03) nanophosphors were co-precipitated uniformly using a homogeneous co-precipitation process. With an excitation wavelength λ ex of 455 nm, the YAG:Ce phosphors showed strong luminescence with maxima at 550 nm in the range of 475–650 nm. The emission intensity becomes stronger due to the improved crystallinity and decreased surface defects of the resultant phosphors with increasing calcination temperatures. The quenching concentration of Ce3+ was 1.5 at% and the quenching mechanism was Ce–Ce interactions and lattice defects. The fluorescence lifetime of the phosphors decreased with increasing Ce concentrations and temperatures. The mechanism is influenced by defects both in surface and body. The resultant YAG:Ce powders showed an excellent sintering activity and can be sintered into transparent ceramic under vacuum technique. Compared with the phosphors, the transparent ceramic exhibits stronger luminescence properties and shorter fluorescence lifetime. [ABSTRACT FROM AUTHOR]

By pre-treating and component design of the ceramic powders, cubic (Lu,Gd) 2 O 3 :Eu solid-solution ceramics with high optical quality were achieved by the solid-state reaction method combined with vacuum sintering. The effects of Gd3+ doping (x = 0.05–0.6) on powder characteristics, phase compositions, microstructures and optical performances of the (Lu 0.95- x Gd x Eu 0.05) 2 O 3 ceramics were systematically investigated to obtain the optimum Gd3+ content. The results indicated that the incorporation of moderate amounts of Gd3+ (5–50 mol%) effectively promoted mass diffusion and grain growth during sintering. The 50 mol% Gd3+-doped Lu 2 O 3 :Eu transparent ceramic (using the powder calcined at 1200 °C) sintered at 1750 °C for 5 h exhibited the optimum transmittance of 77.0 % in the visible spectral region (∼1 mm in thickness), which was significantly higher than the reported transmittance of vacuum sintered (Lu,Gd) 2 O 3 :Eu ceramics (less than 65.0 %). Owing to the lower electronegativity of Gd3+ relative to Lu3+, the bandgap energies of the final ceramics decreased gradually with increasing Gd3+ substitution, and the redshift of the CTB centre was observed with more Gd3+ addition. Under CTB excitation, the incorporation of Gd3+ enhanced the red emission intensity and shortened the fluorescence lifetime. • Highly transparent (Lu,Gd) 2 O 3 :Eu ceramics were achieved by pre-treating and component design of ceramic powders. • Gd3+ doping promotes mass diffusion and grain growth during sintering. • The (Lu 0.45 Gd 0.5 Eu 0.05) 2 O 3 ceramic exhibits the transmittance of 77.0 % in the visible range. • Incorporation of Gd3+ results in enhanced luminescence intensity and shortened lifetime. [ABSTRACT FROM AUTHOR]

In the present work, transparent Y 2 O 3 ceramics were prepared via colloidal processing method from nano-sized Y 2 O 3 powders. The effects of triammonium citrate (TAC) on the colloid stability of aqueous suspensions of nano-sized Y 2 O 3 powders were studied. The surface properties of yttria powders were notably affected by the addition of TAC dispersant. The adsorption of TAC on the particle surface shifts the IEP to lower pH values and increases the absolute zeta potential in alkaline region. Rheological characterization of the investigated system revealed an optimal dispersant concentration of 1 wt%, which correlated well with the saturation adsorption of TAC on Y 2 O 3 powder surfaces. The suspensions with solid loadings up to 35 vol% were achieved with further addition of Tetramethylammonium hydroxide (TMAH) into the dispersing system. The consolidated green bodies were treated by cold isostatic pressing to further increase the green density. Transparent Y 2 O 3 ceramics were prepared after vacuum-sintering at 1700 °C for 5 h. The transmittances of the sample were 74.5% at 800 nm and 79.8% at 2000 nm, respectively. [ABSTRACT FROM AUTHOR]

Mono-dispersed spherical Lu 2 O 3 :Eu (5 mol%) powders for transparent ceramics fabrication were synthesized by urea-based homogeneous precipitation technique. The effects of the doped-Eu 3+ on the synthesis of Lu 2 O 3 :Eu particles were investigated in detail. The results show that the doping of Eu 3+ ions into Lu system can significantly decrease the particle size of the resultant precursor spheres. Owing to the sequential precipitation in Lu/Eu system, there are compositional gradients within each of the resultant precursor spheres. Well dispersed, homogeneous and spherical/near spherical Lu 2 O 3 :Eu powders were obtained after calcination at 600–1000 °C for 4 h. The powder calcined at 600 °C shows better sintering behavior and can be densified into transparent ceramic after vacuum sintering at 1700 °C for 5 h. The luminescence properties of the obtained Lu 2 O 3 :Eu powder and transparent ceramic were also studied. [ABSTRACT FROM AUTHOR]

The effects of pre-treating a nano-sized Y 2 O 3 powder with sulfuric acid were studied. Both the structural evolution and sintering behavior as a function of SO 4 2− -ion concentrations were investigated. The surface morphologies and aggregation state of particles were notably affected by the sulfuric acid-based treatment. The powder untreated revealed particle of flat surfaces and sharp edges, whereas the powders with sulfate dosage were composed of round particles of isotropic surfaces after calcination. Dispersive Y 2 O 3 nanopowder with excellent sintering property was obtained by calcinating the powders treated with 7 mol% sulfuric acid. The optimum sulfate dosage can be well correlated with a single layer coverage of SO 4 2− -ions over the particle surfaces, protecting particles from forming hard agglomerates by contributing to mass transportation mechanisms leading to particle coarsening upon calcination. All the ceramics prepared using treated-powders were transparent after vacuum sintering at 1700 °C, whereas it was opaque for the sample without sulfate dosage. [ABSTRACT FROM AUTHOR]