| Summary: | 碩士 === 輔仁大學 === 物理學系 === 92 === Yttrium garnet is an excellent laser host crystal. And we chose Fe3+ to be our active ion. The 99.999 % grade Y2O3’’’’ Al2O3 and Fe2O3 were first removed the water content. The materials were then ball-milled for ten hours, and sintered in a platinum crucible at 1400 ℃ for 8 hours. Those samples were Y3Al5-xFexO12(0≦x≦5) polycrystal. The changes of crystal structure were studied from X-RAY and RAMAN spectrum. The X-ray refraction pattern reveals that all the samples appear as same single phase. From X-RAY and RAMAN, it shows that Fe ions only replace the sites of Al ions, it doesn’t change the original crystal structure of YAG. Magnetic measurements were achieved by using the SQUID. From the SQUID data, the first thing we know is the Curie temperature increases with increasing the concentration of Fe ions. When the Fe concentration lower than x=2.5, the crystal will turn into paramagnetism from ferromagnetism.
Then, We have successfully grown single crystal Y3Al5-xFexO12 (0 ≦ x ≦ 0. 2) garnets by using the Czochralski technique. Crystal growth was performed by using an induction furnace and a 30 kW generator. The initial seed was a pure YAG crystal oriented along the c-axis. The pulling and rotation rates were 0.8~1.6 mm/hr and 10~20 rpm under a nitrogen atmosphere, respectively. We used a convex solid-melt interface to grow a series of crystals so that the dislocations and impurities were reduced, as well as the stress, in as-grown Fe:YAG crystals. Samples for spectroscopic measurements were cut out of the boules, and surfaces perpendicular to the c axis were polished. The thickness and diameter of the sample were 1mm and 25mm, respectively. The spectral properties and lattice vibrations were studied by transmittance and Raman spectra. Magnetic measurements were achieved by using the SQUID. From the SQUID data, the magnetization increases with increasing the Fe concentration. From the Raman and transmittance spectra studies, it is clear that doping concentration of Fe3+ does influence the spectra properties and lattice vibrations. The observed spectra can be assigned according to their wave number of 1391, 856, 781 and 294 cm-1 for pure YAG crystal. It shifts to lower frequency after doping the Fe3+ ions. This is due to the increase of the mass of Fe ions. For higher frequency modes than 1391 cm-1, the intensity of frequency peaks decrease with increasing the Fe concentration. The absorption edge at 260 nm for pure YAG shifts to 295 nm for sample with x = 0.2, and the absorption peaks at 408 and 416 nm increase with increasing the concentration of Fe ions.
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