Hydrothermal Fabrication And Luminescent Properties Of Nanosized And Submicrosized YBO₃:Eu With Multifarious Morphologies

The study of properties of phosphors is essential to improve the performance of the high-definition color PDP. Nowadays, (Y,Gd)BO₃:Eu³⁺ is recognized as one of the best commercial red phosphors for PDP due to its high VUV absorbency and extraordinarily high luminescent efficiency under VUV excitation. However, all of these advantages do not make (Y,Gd)BO₃:Eu³⁺ as a desired VUV phosphor because of its chromaticity problem, since phosphors used in PDP are required to possess both high luminescent efficiency and good chromaticity under VUV excitation. In the emission spectra of (Y,Gd)BO₃:Eu³⁺, the emission consists of three main peaks: a typical magnetic dipole transition (⁵D₀-⁷F₁) at 591nm which correspond to orange color, and a typical electric dipole transition (⁵D₀-⁷F₂) at 610nm, 625nm which correspond to red color. In (Y,Gd)BO₃:Eu³⁺, according to the selective rule, the magnetic dipole transition (orange color) is permitted but the electric dipole transition (red color) is forbidden. Therefore, the intensity of red emission of bulk (Y,Gd)BO₃:Eu³⁺ is lower than that of orange one, leading to a poor chromaticity. In this dissertation, through reducing the particle size of YBO₃:Eu to nanosize, which increases the number of atoms on the interface and the degree of atomic disorder, we reduce the crystal field symmetry of Eu³⁺ ions located at the interface of the particles, which makes the (⁵D₀-⁷F₂) transition easier. Consequently, the proportion of red color emission becomes higher, and the chromaticity is improved.With "direct hydrothermal" method at a low temperature of 260℃ for 3 hours, in the absence of any surfactant, template, without milling and post calcination, we prepared multifarious morphologies of YBO₃:Eu, including multicrystal nano-sheet, monocrystal nano-sheet, monocrystal nano-particle, monocrystal nano-plate, monocrystal submicro-plate, monocrystal submicro-rod, monocrystal submicro-tube and micro-flower, micro-downy ball which are self-assembled by orderly nano-sheets. Specially, most of morphologies of YBO₃:Eu particles are prepared for the first time to our knowledge. The resulting products are characterized by X-ray diffraction (XRD),transmission electron microscopy (TEM) and scanning electron microscopy (SEM). All measuring results accord with each other very well.Compared with the solid-state reaction sample (SR), all hydrothermal samples show a remarkable improvement on the chromaticity under 147nm and 254nm excitation. Particularly, some of them have a high luminescent intensity that even higher than SR sample, which changed the actuality that samples prepared by hydrothermal method, especially the nano-sized samples always show a much lower luminescent intensity than the SR one.Finally, in order to make the selected-area electron diffraction images of TEM index completely, we proved that the crystal structure of YBO3 is hexagonal, whosespacegroup is P6c2 and lattice parameter is a=6.454 A, c=8.8lA. Hence, theaccepted hexagonal structure of YBO3 whose spacegroup is ^63/m and lattice parameter is a=3.778A, c=8.8lA is renounced.