Le Zhang,Yue Ben,Hao Chen,Dingyuan Tang,Xianzhu Fu,Rong Sun,Bo Song,Chingping Wong
Highly transparent yttria ceramics were successfully fabricated by vacuum pre-sintering and post hot isostatic pressing (HIP) treatment both under very low temperatures synthesized from powders by a co-precipitated method. The morphologies and microstructures, density and thermal mechanical changes, and optical properties of ceramics under different processing stages were systematically characterized by (F)SEM, TMA, optical microscope and UV-Vis-IR spectrophotometer, respectively. The full densification of yttria ceramics could be achieved just at as low as 1450 °C for 4 h (vacuum pre-sintering) and 1400 °C for 3 h (post-HIP). The fabricated ceramics exhibited a uniform and fine microstructure and high optical performance. The average grain size was as small as 0.74 μm. The in-line transmittance reached 81.7% at 1100 nm (1 mm thickness). The transparent yttria ceramics were attractive without any sintering additives at such low pre-sintering and post-HIP temperatures.
Yb,Ho:Y 2 O 3 ceramics have been fabricated by Spark Plasma Sintering method (SPS). The microstructure and transmittance of the ceramics sintered from 1623 K to 1673 K were analyzed. The highest in-line transmittance of Yb,Ho:Y 2 O 3 ceramic sintered at 1673 K reached almost 83% at 750 nm with the thickness of 1 mm. The absorption spectra , fluorescence spectra and fluorescence decay curve were recorded at room temperature. The Judd-Ofelt parameters Ω 2 , Ω 4 and Ω 6 were calculated to be 8.33 × 10 −20 cm 2 , 1.81 × 10 −20 cm 2 , and 0.82 × 10 −20 cm 2 , respectively. The intense emission cross section of Yb,Ho:Y 2 O 3 ceramic was 3.43 × 10 −20 cm 2 at 2057 nm with full width at half maximum (FWHM) of 208 nm. The results indicate that Yb,Ho:Y 2 O 3 transparent ceramic can be a promising laser gain medium for laser operation around 2 μm.
Y 2 O 3 transparent ceramics were prepared from alcoholic slurries of Y 2 O 3 nanopowders via a slip-casting method to avoid the hydrolysis issue. Polyvinyl pyrrolidone (PVP), polyethylene glycol (PEG) and polyethylenimine (PEI) were used as dispersants to improve the rheological properties of the slurries. It was found that PEI is the most effective dispersant in ethanol. The adsorbed amount of PEI was evaluated by infrared absorption and rheology measurements. Y 2 O 3 slurry with a solid loading of 20.8 vol% and a viscosity of <0.1 Pa s at the shear rate of 10 s −1 was obtained using 1.5 wt% PEI. The slurry yielded a homogeneous green body, and finally resulted in a high-quality Y 2 O 3 ceramic with the in-line transmittance of 80% at 800 nm.
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