| 研究実績の概要 |
(Y0.95-xGdxTb0.05)(OH)CO3.H2O monosheres with the average diameter well controlled in the wide range of 110-590 nm were successfully synthesized via homogeneous precipitation. The nucleation density of precipitation and therefore the average size can be adjusted by the concentration of the urea precipitant and ammonium nitrate mineralizer. (Y0.95-xGdxTb0.05)2O3 ceramics with in-line transmittances reaching 80% were then fabricated via vaccum sintering at 1700 deg C for 4 h of the well-dispersed oxide particles calcined from such basic-carbonate monosheres. Colloidal processing was found to be advantageous over CIP for forming, since it produces dense green bodies of high microstructure uniformity. Localized domains were observed in the green body made via CIP, which sinter in priority than the surrounding matrix and thus produce micro-cracks harmful to the fabrication of transparent ceramics. The optimal Gd content was determined to be 2 at% for the 545 nm green-emission of Tb3+. Besides, with the (Y1-xGdxTb0.05)2(OH)5NO3.nH2O nanosheets as a new type of precursor for well-sinterable oxide powders, single-crystal like transparent ceramics (transmittance: 80-83%) were also fabricated via vacuum sintering at 1700 degC for 4 h. It was found that a lower heating rate of vacuum sintering allows uniform densification of the green body from the surface to interior, and thus produces ceramics of higher transparency. The emission of Tb3+ improves with increasing crystallite/particle size of the powder and ceramic, and has the fluorescence lifetime of about 1.5-2.8 ms.
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