| Summary: | 碩士 === 國立臺灣大學 === 化學工程學研究所 === 93 === Strontium orthosilicate (Sr2SiO4:Eu2+) provides the broadband absorption in UV/Blue region, giving rise to a new phosphor approach for application of GaN-based white LEDs. From the TG/DTA and XRD analysis, the formation of Sr2SiO4 is confirmed to be governed by diffusion controlled mechanism. According to the Brounshtein-Ginstling model, the activation energy is suggested to be 139.6 kJ/mol. A sol-gel process employing citric acid and ethylene glycol as polymerizing agent was developed for synthesizing well-dispersed Sr2SiO4:Eu2+ phosphors. The blue-green band originates from the f-d transition of the Eu2+ ion on the Sr(I) site. On the other hand, the emission of the Eu2+ ion on the Sr(II) site is identified as the yellow band. The excitation spectra monitored at the yellow band also showed broader excitation range than that monitored at blue-green band, implying large crystal field provided by Sr(II) site. With increase of europium concentration in Sr2SiO4, the yellow broadband emission will be more dominate. Sr2SiO4:Eu2+ synthesized at the appropriate condition showed the enhanced luminescent intensity and well dispersed particles with grain size around 150 nm.
The synthesis and modification of red oxide phosphors (Y2O3:Eu3+) were investigated. The nano-sized Y2O3:Eu3+ phosphors synthesized via the sol-gel route showed the enhanced crystallinity and luminescent intensity. The europium ions of the sol-gel derived phosphors calcined at 1200℃ are in a more asymmetric environment than those calcined at other temperatures, resulting in the strongest emission intensity at 611 nm. The particles after Li+ ions doping had the advantages of enhanced the crystallinity, improved morphology, and emission intensity. It implies that oxygen defects created after Li+ ions doping would lead to lowering symmetry, resulting in enhanced the 5D0→7F2 electric-dipole emission (611 nm).Tin oxide was used as the coating material on the Y2O3:Eu3+ phosphor. At high current density, the brightness of the uncoated phosphor was quickly saturated. On the other hand, the CL intensity of SnO2-coated Y2O3:Eu3+ phosphor still increased monotonously, suggesting the removal of charge on the surface by conductive material effectively.
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