Highest In-line Transmittance Research Articles

Manufacture and Faraday magneto-optical effect of highly transparent novel holmium aluminum garnet ceramics

A novel transparent magneto-optical holmium aluminum garnet (HoAG) ceramic with a high in-line transmittance of ~80.3 % at 589 nm (~97.0 % of the theoretical transmittance of HoAG single crystal) and a maximal infrared cut-off at ~6.5 μm was successfully fabricated by vacuum sintering at 1650 °C. The facile co-precipitation strategy was employed to yield the precipitation precursor with hollow structures upon calcination into the sphere-like HoAG particle with a narrow particle distribution. Silica sintering aid creates point defect of Ho3+ vacancies to promote the HoAG densification rate during sintering by Si4+ substitution for Al3+ in tetrahedrally coordinated 24 (d) sites. The magneto-optical HoAG ceramic has Verdet constants of ~-154 rad/(T·m) at 635 nm and ~-36 rad/(T·m) at 1064 nm, which are higher than or similar to that of the commercial TGG single crystal. The thermal conductivity of the transparent HoAG ceramic was determined to be ~10.5 W/(m·K) at room temperature.

Fabrication, optical and luminescence properties of low pressure injection molded YAG:Ce tubular ceramics for outdoor lighting

Elaborating a high performance and thermostable LED lighting source based on YAG:Ce ceramic photo-convertor is mainstream for outdoor lighting. However, it still suffers from narrow luminous angle using traditional molding method. In this paper, high quality YAG:Ce tubular ceramic was prepared using a low pressure injection molding (LPIM) and vacuum sintering. The results showed the viscosity of suspension with 75.0 wt.% solid content was as low as 190.34 Pa·s at the shear rate of 100 s−1, and the molding pressure and holding time were adopted to be 0.8 MPa and 8 s, respectively. Impressively, the final YAG:Ce ceramic (double polished to 1.0 mm) with relatively high in-line transmittance of 72.5 % was produced. Furthermore, constructing the YAG:Ce ceramic tube with the hexahedral “columnar blue chip arrays’’, a 4π white light emission with a luminous efficiency of 126.46 lm/W and low correlated-color temperature of 4333 K and was attained.

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.

A novel spinel-type Mg0.55Al2.36O3.81N0.19 transparent ceramic with infrared transmittance range comparable to c-plane sapphire

A novel Mg0.55Al2.36O3.81N0.19 transparent ceramic with an infrared transmission range comparable to c-plane sapphire was prepared based on the intentional design of the composition. This material possesses outstanding optical properties, such as a high in-line transmittance up to 86.5% at 3.7 µm, a refractive index of 1.7240 at 589.3 nm and an absorption coefficient of 0.8 cm−1 at 5 µm. The effects of chemical composition on the crystal structure and optical properties of spinel material were discussed. In particular, the chemical bond strength of disordered tetrahedron varying with the composition largely determines the infrared transparent range of transparent ceramic.

Contamination Study of Zirconia on the Densification Process and Properties of Transparent MgAl₂O₄ Ceramics.

In this paper, transparent magnesium aluminate (MgAl2O4) spinel ceramics are fabricated through pressureless sintering combined with hot isostatic pressing (HIPing). To investigate the effect of zirconia on sintering behavior, microstructure, and optical properties of transparent spinel ceramics, different contents of zirconia were added. The results show that zirconia can promote the densification process by the formation of anion vacancies. The resulting zirconia exists as tetragonal phase along the grain boundaries. The average grain size of resulting ceramics depends on the content of zirconia and HIPing condition. Small zirconia content did not deteriorate the optical properties of samples. A 5-mm-thick sample with 0.05 wt% ZrO2 pre-sintered at 1500 °C followed by HIPing treatment at 1550 °C achieved a high in-line transmittance of 75.5% at 400 nm and 85% at 1100 nm.

A new and highly active sintering additive: SiO2 for highly-transparent AlON ceramic

In the present work, highly-transparent aluminum oxynitride (AlON) ceramic has been fabricated by hot isostatic pressing sintering method. SiO2 was used for the first time as a sintering additive for producing highly-transparent AlON ceramics where it plays an effective role to promote the densification during hot isostatic pressing sintering. Furthermore, the optical property of the AlON ceramic is not sensitive to the change of additive concentration when SiO2 was used. All the 3.5 mm thick samples doped with 0.15 wt% ∼0.55 wt% SiO2 showed a high inline transmittance above 86% at 2000 nm. The effects of SiO2 on the phase, lattice parameter, microstructures and hardness of AlON have been investigated in details.

Uniform and fine Mg-γ-AlON powders prepared from MgAl2O4: A promising precursor material for highly-transparent Mg-γ-AlON ceramics

High-purity and sinterability Mg-γ-AlON (Mg0.1Al1.53O1.89N0.27) powders were synthesized by gas pressure sintering (GPS) of mixed powders of commercial Al2O3 and AlN, and lab-made MgAl2O4. The Mg-γ-AlON powders exhibited a uniform particle morphology and a small particle size of d50 = 3.4 μm, owing to the use of MgAl2O4 as the Mg source. Highly-transparent Mg-γ-AlON ceramics were fabricated using the synthesized Mg-γ-AlON powders by spark plasma sintering (SPS) at 1800 °C for 5 min under an axial pressure of 80 MPa, followed by hot isostatic pressing (HIP) at 1800 °C for 2 h under a nitrogen gas pressure of 190 MPa. The ceramics showed a high in-line transmittance of ∼ 80.5% at 450 nm, ascribed to the high sinterability of the MgAl2O4 raw powder that leads to a pore-free and fully densified microstructure. This indicates that MgAl2O4 as sintering additive is superior over MgO and MgF2 in the fabrication of Mg-γ-AlON transparent ceramic.

Fabrication and optical properties of highly transparent MgO ceramics by spark plasma sintering

Highly transparent MgO ceramics have been prepared via Spark Plasma Sintering (SPS) at 1200°C for 10–60min, under a pressure of 100MPa. All of the prepared ceramics were visually transparent and exhibited relatively high in-line transmittance. The ceramic sintered for 60min demonstrated the highest in-line transmittance, of 60–80% in the 300nm to 9μm wavelength range; values that are close to that reported for MgO single crystals. Photoluminescence measurements revealed a peak located at ~360nm, which was determined to be due to oxygen vacancy color centers induced by the reducing atmosphere of the SPS process in vacuum atmosphere.

Pump laser induced photodarkening in ZrO2-doped Yb:Y2O3 laser ceramics

5 at.% Yb:Y2O3 transparent ceramics were fabricated using vacuum sintering plus HIP. The ceramics doped with 1 at.% ZrO2 as the sintering additive were densified at 1700 °C in vacuum followed by HIPing at 1775 °C, while those without sintering additives were densified at 1520 °C in vacuum followed by HIPing at 1450 °C. After sintering, both ceramics had relatively high in-line transmittance. However, during laser experiments, the ZrO2-doped Yb:Y2O3 (Zr-YbY) ceramics were photodarkened when irradiated by 940 nm pump light. The discoloration might be attributed to the formation of Zr3+ color centers during lasing. In contrast, no photodarkening effect was detected in the pure Yb:Y2O3 ceramics without sintering additives (P-YbY). The P-YbY ceramics exhibited much higher lasing efficiency (17%) than the Zr-YbY ceramics (9%). To our best knowledge, it is the first time that the photodarkening effect was detected in rare-earth doped sesquioxide laser ceramics.

Fabrication of Yb-doped Lu2O3-Y2O3-La2O3 solid solutions transparent ceramics by self-propagating high-temperature synthesis and vacuum sintering

A comparative analysis of sintering and grain growth processes of lutetium oxide and lutetium-yttrium-lanthanum oxides solid solutions, as well as optical properties, luminescence and laser generation of (LuxY0.9-xLa0.05Yb0.05)2O3 transparent ceramics are reported. Fabrication of highly dispersed initial powders of these compounds was performed via nitrate-glycine self-propagating high-temperature synthesis (SHS) method. The powders were compacted at 300 MPa and vacuum sintered at temperatures up to 1750 °С. Optical ceramics of (Lu0.65Y0.25La0.05Yb0.05)2O3 elemental composition were shown to have the highest in-line transmittance, which achieved 78% at the wavelength of 800 nm. Generation of laser radiation at a wavelength of 1032 nm with the differential efficiency of 20% was demonstrated in the (Lu0.65Y0.25La0.05Yb0.05)2O3 ceramics.

Fabrication and Phase Transition of La2-X Lu x Zr2O7 Transparent Ceramics

Materials with A2B2O7 formula have been drawing the attention of researchers for a diversity of applications, such as fast-ion conductors, photocatalysts, thermal barrier coatings, matrices for immobilization of highly active radionuclides from nuclear wastes and host materials for scintillators. A2B2O7 materials have three crystal phases decided by the ionic radius ratios (r A/r B). According to the rule of Subramanian et al [1], pyrochlore phase was favored when r A/r B lay within the range of 1.46~1.78. Defective fluorite phase is stable for r A/r B < 1.46, whilst the monoclinic phase is stable for r A/r B > 1.78. In this study, a new series of La2-x Lu x Zr2O7 (x = 0~2.0) transparent ceramics [2] with high density and average atomic number, which are hoped to be scintillator matrix, were fabricated by vacuum sintering and an interesting phenomenon was found. As Lu content increased, the crystal phase gradually transformed from pyrochlore to defective fluorite phase with the existence of a two-phase region (x = 0.6 ~ 1.2) (Figure 1). The appearance of a two-phase region illustrated that Subramanian’s theory is not available when there is large difference in ionic radii of the elements that occupy at Ln position (r La 3+ = 1.160 Å, r Lu 3+ = 0.977 Å). In addition, the grain growth of pyrochlore phase was inhibited due to the appearance of defective fluorite phase. Grain sizes of samples dominated by pyrochlore phase were 11~14 μm. Samples with two phases (x = 0.6~1.2) have much smaller grain sizes (< 3 μm), while samples dominated by defective fluorite phase have larger grain sizes (82~60 μm). All the samples (except for x = 0) are transparent and the highest in-line transmittance is reached to 72.4% (1100 nm) at x = 1.2 though two phases coexist. To verify that the two-phase region was not an accident, we fabricated LaLuZr2O7 powder by combustion method instead of solid state reaction and sintered in the same way. From XRD results, two phases are observed in both the synthesized powder and ceramic. Also, With 2 ~ 3 μm average grain size, the LaLuZr2O7 ceramic reaches high transparency with an in-line transmittance of 73.4% at 1100 nm, which is slightly higher than that made by solid state reaction method, showing the advantage of combustion method in synthesizing good powder. Rayleigh-Gans-Debye scattering theory was used to explain the high transmittance of the ceramics with two phases. When the refractive indices of the coexisting two phases are close to each other and the average grain size is smaller than 10 μm, the two phases have little influence on transparency of the ceramics. [1] Subramanian MA, Aravamudan G, Subba Rao GV. Oxide pyrochlores-A review. Prog Solid State Chem 1983, 15: 55-143. [2] Z.J. Wang, G.H. Zhou, X.P. Qin, F. Zhang, J.P. Ai, P. Liu, S.W. Wang. Fabrication and phase transition of La2-xLuxZr2O7 transparent ceramics. J Eur Ceram soc 2014, 34: 3951–3958. Figure 1

Influence of solid loading on the rheological, porosity distribution, optical and the microstructural properties of YAG transparent ceramic

Stable aqueous dispersed mixture of commercial Al2O3 and Y2O3 nano powders was prepared by ball mill. Ammonium poly meta acrylate (Dolapix CE64) and tetraethyl orthosilicate (TEOS) were added as dispersant and sintering aid, respectively. The effects of slurry solid loading on the fabrication of transparent polycrystalline YAG ceramics by slip casting method were investigated. The rheological properties of slurries with different solid loading (64, 70 and 76 wt%) were studied by measuring the viscosity and shear stress as a function of shear rate. The effect of solid loadings on the porosity distribution was examined. The specimens were vacuum-sintered at 1715 °C for 10 h. Slips with 64 and 70 wt% solid loading behaved as near-Newtonian and as non-Newtonian with thixotropic behavior at 76 wt% solid loading. The relative densities of the green bodies increased from 58.0 ± 0.6% (SD = 0.424) to 64.0 ± 0.3% (SD = 0.228) by increasing the solid loading from 64 wt% to 70 wt% and then decreased to 63.0 ± 0.2% (SD = 0.141) at 76 wt% solid loading. The results showed that the suitable solid loading for fabricating transparent YAG ceramics is 70 wt%. This sample had the narrowest pore size distribution (4–100 nm), homogenized surface fracture of green body, dense microstructure (99.990 ± 0.005% final relative density, SD = 0.003) and the average grain size of 6 µm. It had the highest in-line transmittance, which was approximately 77% at 1064 nm.

Gel-casting of transparent magnesium aluminate spinel ceramics fabricated by spark plasma sintering (SPS)

In this paper, a transparent magnesium aluminate spinel ceramic was fabricated through the newest colloidal gel casting method, using a synthetic powder with the average particle size of 90nm and Isobutylene-Maleic Anhydride (ISOBAM) additive. ISOBAM served as both a dispersant and a gelation agent to achieve a dense body. Also, the suspension rheological behavior was optimized by the solid loading of 85wt%, the additive content of 0.7wt%, and the gelation time of 350s. This led to a green body with a density equal to 65% of theoretical density and the green strength of 14.48MPa. The results revealed that the reduction of porosity and the uniform distribution of pores in the green body (smaller than half of the initial powder particle size, 35nm), as accompanied by spark plasma sintering (SPS), resulted in the final body density of 99.97%, as well as the high in-line transmittance of 86.7% at the wavelength of 1100nm.

The microwave dielectric properties of transparent ZnAl2O4 ceramics fabricated by spark plasma sintering

The transparent ZnAl2O4 ceramics were fabricated by spark plasma sintering. The effects of sintering temperature on the microstructure, optical, microwave dielectric and mechanical properties of ZnAl2O4 ceramics were investigated. With increasing temperature from 1240 to 1280 °C, the average grain size increased from 0.35 to 0.76 μm, and the in-line transmittance increased first and then decreased. The highest in-line transmittance of 64% at 550 nm was obtained at 1260 °C. The quality factor (Q·f) and dielectric constant (er) values increased to the maximum and then decreased with the increase of temperature. The optimal microwave dielectric properties were achieved by sintered at 1260 °C with er value of 8.71, Q·f value of 64,395 GHz, and τf value of −68 ppm/°C. The Vickers hardness depended on the relative density and the grain size, and the maximum value of 16.3 GPa was achieved at the sintering temperature of 1260 °C. The transparent ZnAl2O4 ceramics with good microwave dielectric properties would be a new optical-electronic integration material.

Fabrication of transparent MgAl2O4 spinel through homogenous green compaction by microfluidization and slip casting

In this study, a transparent magnesium aluminate (MgAl2O4) spinel prepared by homogeneous green compaction and sinter-HIP processes was investigated. The uniformity of the particle configuration in a green body could be improved by both a wet shaping via slip casting and a microfluidization process, which effectively disintegrates particle agglomerates in aqueous slurry by passing the material through a narrow channel with a high shear stress. The relation between the green body state and the sintering behavior showed that the densification during pre-sintering was accelerated by reducing the mean pore size in the green body, which resulted in a finer microstructure. After post-HIP processing, the final grain size and the in-line transmittance was found to be significantly affected by the pre-sintered state. A high in-line transmittance (ILT=79.3% at λ=550nm) was achieved in the specimen fabricated via microfluidization and slip casting.

Optical enhancement brought by doping Gd(3+) ions into Ce: YAG ceramics for indoor white light-emitting diodes.

We dope Gd(3+) ions into Ce: YAG ceramics to induce red-shift in the photoluminescence, of which the degree is proportional to the Gd(3+) doping concentration. This kind of ceramic, when collaborating with InGaN blue chips, proves to be a promising fluorescent material of white light-emitting diodes, for not only its high in-line transmittance and decent quantum yield, but also the improvement in color rendering ability brought by the red-shift, which enhances the ratio of red portion in spectra. We demonstrate that 10% is the optimized value of Gd(3+) doping concentration, as it provides the maximum color rendering index of ~78 with luminous efficiency as high as 128 lm/W.

Optical properties and laser oscillation of Yb3+, Er3+ co-doped Y3Al5O12 transparent ceramics

We reported a kind of Yb3+ and Er3+ co-doped Y3Al5O12 (Yb, Er:YAG) transparent ceramics fabricated by using one-step vacuum sintering. The decent optical properties of the samples, e.g., high in-line transmittance up to 83.4% (at 1.6μm), are benefit from their fine structures, in which the average grain size is 15μm, without any pores spotted within the scope. The absorption around 970nm of this co-doped ceramic reaches nearly 4.8 times that of the single Er3+ doped YAG. Laser operation at 1645nm was evaluated by using a commercial laser diode emitting at 970nm. The maximum output power of 155mW was acquired with an optical-to-optical efficiency of 2.8%.

Fabrication and properties of La2-xGdxHf2O7 transparent ceramics

La2-xGdxHf2O7 (x=0–2.0) transparent ceramics were fabricated through vacuum sintering from nano-powders synthesized by a simple combustion method. The phase composition of the powders and final ceramics, the in-line transmittance, microstructures and density of the ceramics were investigated. With the increasing of Gd content, the ceramics maintained the cubic pyrochlore structure, and the lattice parameters decreased, whilst the densities increased linearly. All the ceramics were transparent. The highest in-line transmittance was 76.1% at 800nm (x=1.2). With high density (7.91–8.88g/cm3) and effective atomic number, some of the La2-xGdxHf2O7 (x=0–2.0) transparent ceramics are promising candidates for scintillator hosts.

Transparent La2−xGdxZr2O7 ceramics obtained by combustion method and vacuum sintering

Abstract Transparent La 2 − x Gd x Zr 2 O 7 ( x = 0–2.0) ceramics were prepared via vacuum sintering from nanometric powders synthesized by a simple combustion method. The changes of phase composition, morphology and in-line transmittance of the resulting ceramics with Gd 3+ content’s variation were investigated. With the increase of Gd 3+ content, the samples keep the pyrochlore structure, but the X-ray diffraction peaks of the powders and ceramics shift to higher angle as the lattice parameters become smaller. All the ceramics are transparent with high in-line transmittance and high refractive index (2.08 @ 632.8 nm, x = 0.4–1.6). These results indicate that La 2 − x Gd x Zr 2 O 7 ceramics might be used as optical lens. Moreover, with the increase of Gd 3+ content, the effective atomic number and density of the ceramics increase, therefore making them promising host candidates for scintillators.

SPS法による高透光性ナノ構造アルミナの合成

Highly transparent aluminas were synthesized by SPS processing under the conditions of 100 MPa and 200°C/min. High in-line transmittances of about 30 % at λ=400 nm and more than 60 % at λ=800 nm were obtained for the aluminas sintered at 1150°C for 10 min-45 min or at 1200 for 10 min. The in-line transmittance monotonously decreases with the increase of grain size in sintered aluminas and it is indicated that high transparency is attributed to both high densification and submicron grains less than 350 nm, which were realized by high heating rate of 200°C/min and high pressure of 100 MPa. Scarce existence of pores in SPSed aluminas was found by TEM observation and it is also responsible for their high in-line transmittance. Further, it is indicated that higher sintering temperature than 1200°C and longer sintering time, except for 1150°C, degrade the transparency of sintered aluminas.