The preparation, characterization, and luminescence of yttrium-based phosphors such as europium activated yttrium oxide (red) and terbium activated yttrium aluminate (green) by sol-gel processes is presented. The sols of yttrium hydroxide were synthesized by various routes. It was found that the sols obtained through an ion exchange column were pure and without any cross contamination. The aluminum hydroxide sols were prepared from aluminum chloride and ammonium hydroxide. A number of gel samples were synthesized by mixing stoichiometric amounts of Y(OH)3 and Al(OH)3 to obtain Y3A15012, Y4A1209, and YAIO3 with trace amounts of rare earth, RE(OH)3 gels as activators. These gels were dried at 30 to 80°C. From the thermal analyses, all possible temperature transitions were identified. After calcination with different temperatures and durations, these phosphor powder samples were characterized for crystallization, spectral energy distribution, and morphology. The samples synthesized at lower temperatures (< 1000°C) were fully crystallized. The average particle size of these phosphors was in the range of 1 to 2 p.m. From the luminescence spectral data, all possible transitions 5D0 -7F12 corresponding to Eu3 in Y203, and 5D4 -* 7F1 6 corresponding to (Th3 ) in yttriumaluminum-garnet (YAG) matrices were identified. The luminescent efficiencies of these phosphors were comparable with commercially available phosphors having larger particles (6 to 10 p.m). The preparation of other yttrium-based phosphors such as YAG:RE3 and Y2SiO5:RE3 (RE = Tm, Ce, Th, and Eu) and the luminescence studies of these materials at low voltages for field emission display applications are in progress.

X-ray luminescence computed tomography (XLCT) is proposed as a new dual molecular/anatomical imaging modality. XLCT is based on the selective excitation and optical detection of x-ray-excitable nanoparticles. As a proof of concept, we built a prototype XLCT system and imaged near-IR-emitting Gd(2)O(2)S:Eu phosphors in various phantoms. Imaging in an optically diffusive medium shows that imaging performance is not affected by optical scatter; furthermore, the linear response of the reconstructed images suggests that XLCT is capable of quantitative imaging.

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X-ray luminescence has the potential to be a promising new modality for enabling molecular imaging within x-ray scanners. Although much work needs to be done to ensure biocompatibility of x-ray exciting phosphors, the benefits of this modality, highlighted in this work, encourage further study.