Preparation and characterization of fine-grain yttrium-based phosphors by sol-gel process

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 Y3Al5O12, Y4Al2O9, and YAlO3 with trace amounts of rare earth, RE(OH)(3) gels as activators. These gels were dried at 30 to 80 degrees 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 degrees C) were fully crystallized. The average particle size of these phosphors was in the range of 1 to 2 mu m. From the luminescence spectral data, all possible transitions D-5(4)-->F-7(1,2) corresponding to Eu3+ Y2O3, and D-5(4)-->F-7(1....6) corresponding to (Tb3+) in yttrium-aluminum-garnet (YAG) matrices were identified. The luminescent efficiencies of these phosphors were comparable with commercially available phosphors having larger particles (6 to 10 mu m). The preparation of other yttrium-based phosphors such as YAG:RE(3+) and Y2SiO5:RE(3+)(RE Tm, Ce, Tb, and Eu) and the luminescence studies of these materials at low voltages for field emission display applications are in progress.