Effects of Gd Substitution on Sintering and Optical Properties of Highly Transparent (Y0.95− xGd xEu0.05)2O3 Ceramics.

Highly transparent (Y0.95− xGd xEu0.05)2O3 ( x = 0.15-0.55) ceramics have been fabricated by vacuum sintering at the relatively low temperature of 1700°C for 4 h with the in-line transmittances of 73.6%-79.5% at the Eu3+ emission wavelength of 613 nm (~91.9%-99.3% of the theoretical transmittance of Y1.34Gd0.6Eu0.06O3 single crystal), whereas the x = 0.65 ceramic undergoes a phase transformation at 1650°C and has a transparency of 53.4% at the lower sintering temperature of 1625°C. The effects of Gd3+ substitution for Y3+ on the particle characteristics, sintering kinetics, and optical performances of the materials were systematically studied. The results show that (1) calcining the layered rare-earth hydroxide precursors of the ternary Y-Gd-Eu system yielded rounded oxide particles with greatly reduced hard agglomeration and the particle/crystallite size slightly decreases along with increasing Gd3+ incorporation; (2) in the temperature range 1100°C-1480°C, the sintering kinetics of (Y0.95− xGd xEu0.05)2O3 is mainly controlled by grain-boundary diffusion with similar activation energies of ~230 kJ/mol; (3) Gd3+ addition promotes grain growth and densification in the temperature range 1100°C-1400°C; (4) the bandgap energies of the (Y0.95− xGd xEu0.05)2O3 ceramics generally decrease with increasing x; however, they are much lower than those of the oxide powders; (5) both the oxide powders and the transparent ceramics exhibit the typical red emission of Eu3+ at ~613 nm (the 5D0→7F2 transition) under charge transfer (CT) excitation. Gd3+ incorporation enhances the photoluminescence and shortens the fluorescence lifetime of Eu3+. [ABSTRACT FROM AUTHOR]